name the apk MPDroid instead of MainAcitvity
show album artist on NowPlaying and according cover
don't show artist if empty, don't show both if albumarist==artist
make showing album artist an option
make albumartist cover show up on playlist
show albumartist cover in NowPlayingSmallFragment, too
Merge pull request #318 from hurzl/newup2

name the apk MPDroid and show album artist on NowPlaying