The following bugs should have been fixed:
* The PlaybackManager no longer starts playing again after
PlaybackManager.stop() has been called.
* The PlaybackManager will no longer get into an invalid state when
next() is called many times fast.
* The PlaybackManager now exposes its error information when the
PlaybackUrl could not be fetched.
* The PlaybackManager will keep a playbackState of Playing as long
as it is not stopped and while in a playlist. Previously, it would
stop and start everytime the next item got loaded.
* Show the now playing cover when playing an item, otherwise show the
collection cover.
* ItemModelLoaders now correctly expose list properties of non-built-in
Qt objects
* toString is now implemented for lists, fixing some query
construction code.
* PlaybackManager now clears the playlist when playing a single item to
prevent weird behaviour.
* The covers are slightly updated.
Besides MPRIS support, this also adds support for hasPrevious() and
hasNext() in several parts to determine whether the
player/playlist/shuffler has a previous or next item.