nowplaying: Improve clickable link search in Now Playing bar.

* The "album" link now searches for any matching tracks of the same album,
  even with different artists.
* The search applies to the playlist that is selected, even if you're
  playing from a different playlist.
* The playing item is reset to the Collection List when the "return to
  playlist" link is selected rather than pulling from the internal
  search playlist (which is likely to be destroyed by a subsequent
  search).