Live Viewer Intensity Plot recalculates when images modified

[MikeSullivan7]

Issue Closes #2490

Description

The Live Viewer now keeps track of the Updated Image List and compares it to the new Image List when changes are made in the directory. This allows the LV to detect if more than one image has appeared at a time, or if any number of images have been deleted and recalculate the mean if this has happened. The update_image_list() method in the presenter is now put on a QTimer as when a large number of images are deleted or changed, it can take long enough that update_image_list() could be triggered multiple times in short succession which lead to peoples with the QThreads.

Developer Testing

make check
make test-system

Acceptance Criteria and Reviewer Testing

• Unit tests pass locally: python -m pytest -vs
• Open the LV with some images in the directory
• Add and delete images of various quantities in the directory and check that the Intensity Plot updates accordingly.

Documentation and Additional Notes

• Release Notes have been updated

[coveralls]

coverage: 72.627% (-0.02%) from 72.645%
when pulling bda5df1 on 2490_LV_images_modified_intensity_plot
into fa2343c on main.

[samtygier-stfc]

Looks good, and seem robust in my testing on linux