TODO

Toto list:

* finish MPRIS2 support (current position and seek)
* restore track position on quit and start
* support albums with multiple discs
* improve management of album from various artists
* fix all albums model when new albums are added
* incremental changes from Baloo (new tracks, modified tracks, removed tracks)

* support multiple selection with Ctrl+Click
* improve and measure test coverage
* improve the album list view (consistency with the other views)
* add drag and drop to the play list
* bring back UPnP support
* add support to cancel at least some operations on play lists
* not blocking models (currently all authors and all albums models blocks the UI when they are filled in