Add persistent playlist mode for cpu-controller and "play later" button

[dascritch]

• [ ] Create persistent playlist mode, I.e. cpu-controller continue to play an audiotag from a removed cpu-audio
  • [ ] Add an attribute exclusive to cpu-controller, or use global parameter
  • [ ] Store playlist
  • [ ] Recall playlst
• [ ] Add a button "add this track to my playlist"
• [ ] Add a button "remove this track from my playlist"
• [ ] Document API
• [ ] Write example page