This was very poorly implemented and can't stay as it is right now:
 - Every second or so the art image was being loaded from disk, scaled,
   base64 encoded and sent over the freakin network!
 - The Android interface didn't take into account small screens, and
   adding the image would cut stuff out of the screen.
 - Didn't manage "edge cases" like playing a song without cover after one
   with cover (previous image was still being shown) or changing players.

This reverts commit e66096d0.

# Conflicts:
#	plugins/mpriscontrol/mpriscontrolplugin.cpp