[LMP] Moved PlaylistModel to a separate header/cpp.
[LMP] Instant queue managing options for #1228.
[LMP] Take instant queue into account on playback for #1228.
[LMP] Show instant queue positions in playlist delegate for #1228.
[LMP] Instant queue management actions for #1228.
Merge branch 'master' of github.com:0xd34df00d/leechcraft
[LMP] Keep stop source & oneshot queue for #1228.
[LMP] Removed seemingly useless null pointer check.
[LMP] Don't double-add the same source to oneshot queue.

This is hopefully the commit that closes #1228.