Properly (re)name the gui's XML elements to suggest their meaning.

Group the gui's bottom components together into the Navigation widget.
This serves the purpose of making the interface more compact, and the
mouse navigation easier.

Shrinking the gui's window should not clutter or overlap elements.  A
minimum size should be respected to allow displaying every widget.

The bottom components are put into individual sets that can be hidden
independently.

Enable floating Navigation and Codec widgets, and allow to dock them
up/down and left/right respectively.  Also allow the Toolbar to dock
both up/down and left/right.

Add a close button to the Navigation and Codec Options widgets, and
enable context menus in the widgets main Menu, Toolbar, Navigation,
and Codec Options.  The View->Toolbars->Navigation menu option will
toggle the Navigation visibility, hiding all of its components.

Allow to select and copy into the clipboard current time, total time,
selection duration, marker A time, and marker B time by highlighting
the content of their own element.

Redesign current time, marker A time, and marker B time elements to
combine action buttons and text fields.

This design fixes the displaying of the selection duration's seconds,
that were cut due to insufficient space for the label element.

Follow the convention dictated by T_vumeter.{cpp,h}.

Docking features require the presence of the title bar.

Bottom dock widgets have been combined into the Navigation widget as
frame elements.  Remove residual code about setting title bars.

Bottom dock widgets have been combined into the Navigation widget as
frame elements.  Remove residual code about checking heights.

Buttons float/dock and close to the left, add a title if set.  Use the
title's mnemonic & to switch to float/dock state.

This solves the problem of Light and Dark themes that do not read dock
widgets mnemonic correctly, putting a & into the widget's title.

Slightly darkening the Light theme windows' background helps to spot
the dock widgets' resize handle, otherwise not visible enough.

Add new hideable items and resort Toolbars order, bottom dock widgets
have been combined into the Navigation widget as frame elements.

Initialize new hideable items visibility, the Navigation dock widget
contains new frame elements.  Sort top to botton following the gui.

Use the status bar as a XML widget.  The status bar can be hidden via
'View->Toolbars->Status Bar'.

The gui interface has space for a taller volume meter.

Reading left-to-right, the segment A to B has the former letter before
the latter.  It makes sense to express this positioning in the goMarkA
icons (A< vs >A, where goMarkB is >B, to represent the segment A<->B).

Visually center the letter B in its box.

The 'Total Time' has been converted into a text field, its content can
be highlighted and copied to the clipboard, there's no longer the need
to prefix the content with ' / ' label, update the code accordingly.

The 'Selection Duration' has been converted into a text field, its
content can be highlighted and copied to the clipboard, update the
code accordingly, there's no longer the need to prefix the content
with 'Selection:' label.

The 'Jump to Marker A/B' buttons has been converted into text fields,
update the code accordingly.

Do not disable the selection duration field when there's no media
loaded.

There sould be no need to set a fixed width, it interferes with the
element due to presence of the combined action button.

This allows to edit marker A/B time via the existing 'Go to Time'
dialog (already used to edit the current time).

When setting a Marker A/B time directly, it may be useful to have a
dialog title describing the action.

The 'Jump to Marker A/B' buttons has been converted into text fields,
update the code accordingly.

With being unable to seek beyond the last frame, the reset marker B
button is useful to put the marker B at total time position (beyond
the last frame).

To put the marker B at total time position (beyond the last frame),
set the marker A, then reset the marker B.

The reset marker A button resets to position 0, the B button to the
position just after the last frame (aka infinite).

The presence of the reset marker A/B buttons also give a hint about
when the markers are unset, that is when a button is grayed out.

$ cd avidemux_core/ADM_coreUtils/src
$ nano prefs2.conf
$ chmod +x update_prefs.sh
$ ./update_prefs.sh

Modifying the selection duration will shift the marker B.

i.e. marker B = marker A + selection duration

Modifying the total time will set the marker A to the new duration and
reset the marker B, selecting the last part of the video that once cut
will give the new total duration.

i.e. marker A = new total duration, marker B = old total duration

Save the visibility state of each widget set as preferences.

Individual sets in the Navigation dock can be hidden or not,
then after a restart the previous state is restored.

The Navigation dock can be hidden without changing the state
of its children.  The previous condition will be remembered.

$ cd avidemux_core/ADM_coreUtils/src
$ nano prefs2.conf
$ chmod +x update_prefs.sh
$ ./update_prefs.sh

When a dock widget visibility is toggled via a method, like context
menu, which is not its toolbar checkbox, use a workaround to update
the state of the toolbar checkbox.

Override the application default context menu.  Right clicking on the
menu bar, tool bar, or dock widgets will open Views->Toolbars menu.

A uint64_t type cast gives the right precision to uint32_t values when
converting to a hh:mm:ss.mm,us time expressed in microseconds.

New ADM_QLineEditPTS class to add precision to time fields.  GUI text
elements now store time at microsecond precisions.  This prevents the
jittering bug when switching focus out from a time field.

Jittering bug: Time fields signal editingFinished after switching the
focus or pressing Enter.  Fields signaled as edited are compared with
the previous real time to confirm that they have been truly modified.
A field time is converted from milli to the micro seconds of the real
time.  The equality fails when the real time microseconds part is not
all zero.  The jitter is when the field time, differing from the real
time, is replaced with the closest frame real time (usually the frame
before).

Thanks to szlldm for spotting the jittering bug.

Thanks to eumagga0x2a for fixing obsolete regexp code.

Editing the markers A/B fields directly, by changing the text, may
result in a computed frame real position not diffrent from before.

Different timings may resolve to the same frame.  When an A/B text
refresh is not performed anyway, the edited value may be obsolete.

Editing A/B directly is more flexible than the 'Go to Time' dialog
but, as said before, the difference is that the former changes the
field text before the frame computation is done, the latter intead
changes the text after, and only if the computed time differs from
the currently one set.

Confirming the total time edit should be followed by a refresh.

The total time field can be edited to prepare a cut selection from the
marker A to B starting from the end of the video.  This feature can be
used to set a cut to reduce the video length of a specific amount.

After refreshing the total time field, the video length specified will
be indicated by the marker A time.

Time fields will show microsecond precision timings when hovered,
i.e. 99:59:59.999,999.  Tooltips will be updated when a field has
been programmatically changed, or a user's edit is confirmed.

This could also be used for debugging purposes.

$ cd avidemux_core/ADM_coreUtils/src
$ nano prefs2.conf
$ chmod +x update_prefs.sh
$ ./update_prefs.sh

This is a workaround about editingFinished events.  Even when time
fields are set to readonly, the signal triggers just one time when
the field is clicked and then the focus is changed, with Tab or by
clicking another element.

This could be a better solution than disabling the time fields, if
there are action buttons that should be kept enabled in a field.

Add preference to show only the default action button on time fields
or all the buttons.

Fixes typo in 'Start making use of microseconds precision' commit.

Each time field has a preference option to enable direct keyboard
editing of the field.