DN-MC6000MK2: Sync mapping with push-and-hold

- Use MIDI mapping for "sync_enabled" to support push-and-hold
- Change sync mode indicator LED:
  MASTER=blinking, FOLLOWER=on, NONE=off
- Use setParameter() instead of setValue() for effect parameters
- Fix right effect unit enabled LED
Merge pull request #317 from uklotzde/denon-mc6000mk2-midi

DN-MC6000MK2: Sync mapping with push-and-hold