Applies filter to just show the images in the ImageViewer
Summary:
- adds SortModel in ImageViewer to filter just the images for the ImageViewer listView
- uses filterRole and filterRegExp properties exposed by QSortFilterProxyModel
- mapping from source and to source are done in order to keep the currentItem consistent for every view
Reviewers: Koko, mart
Reviewed By: Koko, mart
Maniphest Tasks: T6268
Differential Revision: https://phabricator.kde.org/D6607