Some more AutoDJ cleanups.

* Move DeckAttributes setup/teardown into a constructor.
* Get rid of group-formatting in AutoDJProcessor.
* Assign DeckAttributes to left/right and this/other local variables to
  keep the code semantic instead of referring to things by index.
* Keep track of DeckAttributes orientation.
Replace CO usage with wrapper functions that describe their meaning.

Drastically improves the readability of the AutoDJ logic.
Remove redundant deck play calls.