Add shuffe / repeat to the player

From the beginning in Moovida there's no way to shuffle or repeat currently playing set.

There are several shuffle / repeat modes that can be useful in different scenarios:
- shuffle by song/video (just play all songs/videos randomly)
- shuffle by album (play the whole album, then randomly switch to another album)
- shuffle by artist (play all albums by an artist, then randomly switch to another artist)
- repeat one
- repeat all

What's more, the shuffle modes could actually be combined to get 'shuffle by artist, then album' or 'shuffle by artist, then album, then song'.

One important thing when shuffling is to cache the shuffled set so that it'd be possible to go back / forward in the playlist and not shuffle on every track change to get better performance.

Also it should be possible to un-shuffle a set.