Player accessibility improvements

Group and re-order playback control elements so that important ones can be accessed more quickly.

There should be enough time to have Voice Over or Switch Control iterate over every element when the player controls are configured to stay on the screen for 20 seconds.

Desired control priority:

1. Play/pause.
2. Next track.
3. Previous track.
4. Exit.
5. Remaining controls, left to right, top to bottom

Scrubbing using Switch Control should be optimized somehow. YouTube has a feature where keyboard keys 1-9 jump through 10%, 20%, etc through the duration of the video. Key 0 is a quick jump to the beginning (i.e. 0%). Having these be switch control actions (and for that matter, mapped to keyboard keys) could make scrubbing to a specific place a little easier.