ImageGallery deletion signal

[servantftransperfect]

Problem:

When deleting an object in the image gallery on a large project, the UI may block for 20 seconds or more.

ImageGallery model is the cameraInit viewpoints attribute (a listAttribute).
When removing an image, listAttribute remove is called.
remove emit valueChanged, which tells the imageGallery that the whole model must be invalidated and reloaded.

I propose to replace the emission of the valueChanged signal with the direct call of the slot _onAttributeChanged.

Does not break the tests, but i am not sure if it does not have any collateral effects.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.74%. Comparing base (910a1ce) to head (a46d81b).
⚠️ Report is 2 commits behind head on develop.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2967      +/-   ##
===========================================
- Coverage    80.76%   80.74%   -0.02%     
===========================================
  Files           59       59              
  Lines         7849     7853       +4     
===========================================
+ Hits          6339     6341       +2     
- Misses        1510     1512       +2     

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