Warn about unsaved data rather than force users to save

[jeylau]

Currently, the GUI cannot be closed unless the user saves the data; this is annoying when using the GUI to only visualize data, or if discarding changes is desired. We now rather open a Warning message box asking confirmation.

Fixes https://github.com/DeepLabCut/DeepLabCut/issues/2042

[deprecated-napari-hub-preview-bot[bot]]

Preview page for your plugin is ready here: https://preview.napari-hub.org/DeepLabCut/napari-deeplabcut/48 Updated: 2022-12-12T14:12:11.304937

[MMathisLab]

looks great! not sure why testing are failing, but once fixed let's merge!

[codecov-commenter]

Codecov Report

Merging #48 (7300afb) into main (23463de) will decrease coverage by 0.20%. The diff coverage is 44.44%.

@@            Coverage Diff             @@
##             main      #48      +/-   ##
==========================================
- Coverage   91.21%   91.00%   -0.21%     
==========================================
  Files          11       11              
  Lines        1275     1279       +4     
==========================================
+ Hits         1163     1164       +1     
- Misses        112      115       +3     

Impacted Files	Coverage Δ
src/napari_deeplabcut/_widgets.py	87.15% <20.00%> (-0.37%)	:arrow_down:
src/napari_deeplabcut/_reader.py	91.51% <50.00%> (-0.51%)	:arrow_down:
src/napari_deeplabcut/_tests/test_widgets.py	100.00% <100.00%> (ø)

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[backyardbiomech]

@jeylau can you propagate this fix over to the main Deeplabcut GUI branch?

[backyardbiomech]

Actually, it works in a labeling window called by the DLC GUI only after I install napari-deeplabcut specifically in the same env.