1922 live view emit dir structure on load

[JackEAllen]

Issue

Closes #1922

Description

View makes a call on initialisation to the model to emit a signal to load images so that if images are already present in the selected directory, they are loaded into the live viewer. Previously Images if present were not loaded into live viewer on initialisation.

Testing

Try loading the image viewer with and without images already populated inside the selected directory.

1. Create a empty directory
2. Load live viewer using CLI flag python -W default -m mantidimaging --log-level DEBUG -lv <LIVE_DIR_OUT/> or from the menu: File>Live Viewer select a folder.
3. Verify that the live viewer window opens with no data loaded successfully
4. Begin copying image files over to the live viewer using the utility script scripts/simulate_live_data.py: python simulate_live_data.py -s ../<LIVE_DIR_IN/>/ -d <../LIVE_DIR_OUT/>/ --faulty
   and verify images display in the live viewer.
5. Close Mantid Imaging and repeat steps with the populated directory verifying that the live viewer shows loaded data on opening.

Acceptance Criteria

• Live viewer opens successfully when selected with an empty directory.
• Live viewer displays images present in a selected directory that already contains images.

Documentation

docs/release_notes/next/fix-1922-live_view_image_load_on_init

[coveralls]

coverage: 76.482%. remained the same when pulling 9e75dd4 on 1922_live_view_emit_dir_structure_on_load into b8a7a2f on main.

[samtygier-stfc]

Fine with the unused function removed.

Wondering if this could just be added directly to ImageWatcher, so that it calls self._handle_directory_change() in its constructor. Is there a time we'd want to create and ImageWatcher and not an immediate file list?