Better Queue management

[vixalien]

Better queue management includes following:

• Add to queue for songs and playlists
• Fetch more queue items for huge playlists
• Sometimes, when changing automatic queues, the track is duplicated (possibly fixed)
• Maybe even allow the Queue to implement the Gio.ListModel interface directly
• Show a context menu for queue items, allowing to like them, etc
• Allow rearranging queue items
• Show the autoplay slider as a GtkSectionTitle
• Allow disabling autoplay
• add menu to now playing menu to allow adding current track to library (and maybe add queue, sleep timer, etc...)

maybe for #30