MPDStatistics: Return null from dbUpdate() if not yet refreshed.
dmix: Repair regressions from 9201c70.

I didn't test commit 9201c70 well (read: at all). This fix retains many of the
ideas from commit 9201c70, while reverting a few.
MPDAsyncHelper: Use album cache by setting.

A regression, most likely from 02c6e3f.
MPD.java: Crop only if the playlist length is greater than 1.
MPDPlaylist: Use status changes to refresh for playlist changes.

Idle playlist subsystem is not the optimal place to check for playlist
updates, it can actually cause huge inconsistencies (as I learned earlier
in 55029f9).
MPDAsyncWorker: Fix a connection detection regression.
Music: Revert "Remove unused inner comparator class."

Please excuse this breif lapse in judgement.
Merge branch 'develop' of https://github.com/abarisain/dmix into develop
Collapsed Albums: add setting
Collapsed Albums: add strings

Conflicts:
	MPDroid/src/main/res/values-de/strings.xml
Collapsed Albums: add PlaylistAlbum
Collapsed Albums: add size() and hasText() to AbstractPlaylistMusic
Collapsed Albums: add CollapsedPlaylistFragment
Collapsed Albums: use CollapsedPlaylistFragment
make playlist text autoscroll
make header in SongsFragment autoscroll
make Songs in SongsFragment autoscroll
autoscroll in albumfragment -- partially
show disc and track number in NowPlaying