Remove non-unique id attributes from UI buttons and add classes instead.
Let the button functionality be initialized by the pattern.

Breaking change:
In this version a pattern handles all the JavaScript functionality to ensure best possible encapsulation between different instances of the datagridfield widget.
If you have customized templates, make sure you do the following:
- Add the class ``pat-datagridfield`` to the ``datagridwidget-table-view`` nodes (files: datagridfield_input.pt, datagridfield_input_block.pt).
- Add the following classes instead of ids to the ui buttons as shown in this map (files: datagridfieldobject_input.pt, datagridfieldobject_input_block.pt_):
    - #btn-addrow -> .dgf--row-add
    - #btn-deleterow -> .dgf--row-delete
    - #btn-moveup -> .dgf--row-moveup
    - #btn-movedown -> .dgf--row-movedown

Change row UI elements from anchor to buttons for better semantics.
Fix Boostrap classes, remove unused attributes, add a title to buttons.

…vent handling.

…ted.

- Factor out countRows function for reuse.
- Bring count field into reach of pattern.

Breaking change:
The JavaScript resources have changed a lot.
Please run the provided upgrade steps!

If you were customizing templates which loaded these JavaScript resources
or customized the JavaScript functionality itself, take special care.
The bundle is loaded only for logged-in users.