Refactor "sibl_gui.ui.cache.AsynchronousGraphicsItemsCache.addContent" method.
Remove unused imports.
Improve images caches code handling consistency.
Implement large thumbnails support skeleton.
Continue large thumbnails support skeleton.
Update caches metrics related code.
Handle third party images formats thumbnails.
Remove attributes in "sibl_gui.components.core.iblSetsOutliner.views.Thumbnails_QListView" class.
Implement thumbnails size handling through nodes instead of model.
Update "Default_Layouts.rc" file.
Remove unused argument in "sibl_gui.libraries.freeImage.freeImage.Image.load" method.
Update "CHANGES.rst" file.
Merge branch 'feature/largeThumbnails' into develop