qt: Revamp playlists on the video and music tab
This patchs contains a revamped Qt Playlist and its distinct views for "Video" and "Music". The Playlists covers are now generated based on their Media(s) thumbnails.
It also packs the following improvements for the CoverGenerator:
- Improve image loading with QImageReader.
- Improve Divide implementation.
- Fix SVG scaling.
Edited by Benjamin Arnaud