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.
QT5 build fixes

load_atomic calls
Transition time fixes.

* Remove transition time UI update for short tracks.
* Fix bug in updating transition time where decks didn't use the latest value.
Remove two more unnecessary deck play calls.
Comment run on AutoDJProcessor.

Left myself some TODOs, pointed out some bugs.
Rename AutoDJProcessor::playerPlayChanged to calculateFadeThresholds to
better represent its purpose.
Fix bug where Fade Now does not use the latest transition time.

The posThreshold calculated in fadeNow assumes the deck's fadeDuration
is up to date.
Some appdata.xml fixes.

* Add name/summary.
* Set metadata_license to CC-BY-SA-3.0.
* Set project_license.
* Add screenshot caption.
* Use component rather than application.
Remove unused files.
Fix AutoDJ empty-queue disabling to update the CO and disconnect signals.
Delete obsolete include directives
Work in progress...