Complete rewrite of the underpinnings of Music
Use persistent list models throughout Music to hold the state of a users music collected through Grilo and Tracker.
The extent of the rework did not allow for a gradual approach, so this commit marks a hard break from the old approach. It is not yet on-par with the old codebase.
This rework is partially based on the work of Jean Felder jfelder@src.gnome.org.
Related: #299 (closed).
!420 (closed) is the non-squash branch of this.
Edited by Marinus Schraal