1. Fix duplicate covers in 'Manage payers' dialog.
2. Fix custom favourite icons being replaced with default cover.
3. Incrementally load playlist track listing, use LMS's "Items Per Page" setting to control batch size. (Will be changed to Material-specific config item for 3.5.0)
4. Only allow editing (in 'Browse' view) of playlists of 250 (or less) tracks.
5. Use custom 'no cover' image in 'Manage players' dialog.