Improve start-up continuity in generated playlist.

[dotson]

Research ways to smooth out playback start-up of of DJ Pedro's playlist for all use cases:

• iTunes is not playing, DJ Pedro begins from a stopped player state.
• iTunes is currently playing a song different from the seedTrack, not in DJ Pedro's playlist.
• iTunes is currently playing a song different from the seedTrack, in DJ Pedro's playlist.
• iTunes is currently playing the seedTrack, not in DJ Pedro's playlist.
• iTunes is currently playing the seedTrack, in DJ Pedro's playlist.

Notes:
Because of the way iTunes 11 handles playlists, there's currently a pause/un-pause coded into DJ Pedro at the start of playback. If Apple ever provides a better way to deal with Up Next, besides GUI scripting, this will be updated.