Don't include flags in configuration change if their value hasn't changed.

This makes the check in updateFrom() match the logic in diff().

Change-Id: I3ab4e8460f7fbf985ef55b9514a8aa90d401d486
Allow adjusting progress on touch events.

Change-Id: Ide0a7ae057a62f3631a32eeaa63f3e04dec5bf54
Prefer artist over album artist.

E.g. when playing a compilation title, one very likely wants to see the real
artist instead of 'Various artists'.

Change-Id: Ie200f2f8b0b90d3470c2e2e4ca6f91f9b117fb1f