MAINT: Split into submodules

[larsoner]

This branch has a git diff cbrnr/restructure that is empty (so should be equivalent), but better blame:

• https://github.com/larsoner/mne-qt-browser/blame/restructure2/mne_qt_browser/_dialogs.py
• https://github.com/cbrnr/mne-qt-browser/blame/restructure/mne_qt_browser/_dialogs.py

@cbrnr WDYT?

Closes #347
Closes #349

Must be merged by rebase rather than squashed to work

[larsoner]

FYI the way to do this quickly was to use the git-split.sh script above, then git checkout cbrnr/restructure <filenames> and commit the result. So @cbrnr your splitting work is implicitly in there still!

[cbrnr]

It's all authored by you?

[larsoner]

Yep. If you want authorship credit you can do in a new branch:

1. Copy the git-split.sh script linked previously to some place you can execute it (and set the execute bit)
2. git-split.sh _pg_figure.py _colors.py etc. repeatedly
3. git checkout origin/restructure <filenames> where <filenames> has all changed files from your existing PR
4. `git commit -am 'FIX: Deletions and insertions'

It's more or less what I did. Should be very quick

[cbrnr]

Superseded by #351.