avoid NPE in Music.getPath()
remove albumartist user option and make getAlbums return merged lists

- return empty List instead of null in getArtists

Conflicts:
	MPDroid/res/values-de/strings.xml
	MPDroid/res/values-fr/strings.xml
	MPDroid/res/values-ru/strings.xml
	MPDroid/res/values-uk/strings.xml
	MPDroid/res/values/strings.xml
Go to Album Artist in NowPlaying

Conflicts:
	MPDroid/res/values-fr/strings.xml
add albumCache and cachedMPD
move Artist.isAlbumArtist to Album.hasAlbumArtist

- adapt equals() for Item merging
- fix sorting albums by artists and albumartists
rework AlbumCache

- add unique album list to cache (enable listAlbumArtists)
- remove albumsByArtist and albumsByAlbumArtists
- remove artistsByAlbum  and albumArtistsByAlbum
replace MPD by CachedMPD (without enabling it)
add option whether to use local album cache

Conflicts:
	MPDroid/res/values/strings.xml
return songs for any artist if only album name is given

for full albums list when not using cache
allow AlbumsGridFragment for full album list when using cache
remove Artist from SongsFragment
adjust Searchactivity
show artists in albums list
fix mopidy behaviour (missing listallinfo)
compare albums by names only to fix duplicates on mpd 0.18
remove songs that don't belong to an albumartist album

mpd >=0.18 puts them in as it takes the artist as the albumartist
if that is not defined
fix string comparisons
add strings for unknowns
 don't filter unknown artists/albums and show them on top of lists

Conflicts:
	JMPDComm/src/org/a0z/mpd/Artist.java
	JMPDComm/src/org/a0z/mpd/MPD.java
	JMPDComm/src/org/a0z/mpd/Music.java
show unknown album text in album grid, too