DeskClock: Bring back Multiplayer and add UI-side support for playlists.

The goal of MultiPlayer was behaving like Music Player: playing random songs,
not repeating one random song infinitely.

Also add UI-part for choosing playlists as a alarm.

Change-Id: I893808421490094531130dfb683ad226df4c91ab
Merge branch 'cm-12.0' into mkl