[Media Controller] Add shuffle and loop controls

Now that we have a footer area, let's put it to good use.

When there is only one player, its name is shown instead of the player bar. Shuffle toggles as usual and Loop cycles between Off, Playlist, Track.

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@ndavis I need an icon media-playlist-repeat-song to indicate the single track repeat mode. We have plenty of icons but all seem Amarok-specific.