Add manual control of Repeat and Shuffle

[jgoguen]

Related to #8 is adding the ability to toggle shuffle and repeat. The play queue should have the following states:

• Shuffle on: randomize the order of the queue every time shuffle is turned on.
• Shuffle off:
  • Version 1: It would be fine to just not change the order of the current play queue for V1 of this feature .
  • Version 2: If playing from a defined playlist (either a playlist, album list, or a future "All Songs" view), turning shuffle off should reorder the queue according to the list display order, with playback continuing from whatever queue position holds the currently playing song. If playing from a queue modified with "Add to Queue", just leave the queue in its current order.
  • Version 3: If the queue was created with "Play Next" or "Add to Queue", reorder the queue according to the order of whatever view it was started with and play back from whatever queue position the current song is at.
• Repeat off: play to the end of the current queue and stop.
• Repeat One: continuously play the current song, only changing if the song is manually changed by the user (by choosing a new song or pressing the Next button).
• Repeat All: play to the end of the current queue; if Shuffle is on randomize the queue order and start from the beginning, or if shuffle is off just go back to the beginning of the queue and continue playback.

When starting playback by choosing a song or pressing Play, the Shuffle state should be whatever it was previously. When starting playback by pressing Shuffle, the Shuffle state should be turned on.

[eeston]

Defs want to add this. At the moment playback issues are my priority. I would like to have a solid foundation before bolting on features.