servicebinder
AlbumCoverHandler: Implement album cover downloader.
AlbumCoverHandler: Don't recycle, just nullify and let GC do it's job.

I'm not sure exactly why but there are some times that Android can get out of
state and will try to parcel the albumCover after recycling. With Android 3.x+
it's really not worth the risk of crashing the service over it, so null it
and let GC do it's job.
ConnectionInfo: Add a class to track the current connection configuration.

This replaces MPDConnectionInfo from MPDAsyncHelper and adds a callback
triggered by connection configuration change. This object also stores
whether where the connection changed since last connection configuration.

This should improve or fix #552.
service: Setup service for ConnectionInfo use.

Since the service is in a separate process, when the connection information is
updated it won't be received as the AsyncHelper and Monitor are running in a
separate process, so we need to send this information over our service binder.
MPDAsyncHelper: Don't allow adding listener multiple times.
AndroidManifest: Format and warning cleanup.
AndroidManifest: WRITE_EXTERNAL_STORAGE permission not required for API 19+.
service: Add a debug boolean for the service module.
MPDroidService: If MPDroid task is swipped to remove, restart service.

This works around the default behaviour that if MPDroid is killed, the service
should be. Since, in this case, the service is a completely separate entity,
restart and get back to where it was on main process task swipe kill.
MPDroidService: More audio focus improvements.