Fix flac files not loading
Merge branch 'master' of github.com:mixxxdj/mixxx
DN-MC6000MK2: Initial revision
DN-MC6000MK2: Map some controls and the VU meter LEDs directly
DN-MC6000MK2: Looping

- Loops: Manual, beat and beatroll
- Censor: Use reverseroll instead of reverse
- Scratching: Don't modify keylock mode
DN-MC6000MK2: Track loading

- Solo cue mix when loading a track (can also triggered manually
  by pressing Shift + Cue Mix)
- Slip mode fixes (still does not always work as expected)
DN-MC6000MK2: Samplers and various improvements

- 16 samplers (4 per deck)
- Hotcue fixes
- Sync mode switching improvements
- Use cue mix LEDs as track load indicator
- Delete obsolete filter controls
DN-MC6000MK2: Polishing

- Global shift state
- Slip mode fixes
- Looping improvements
- Cue button controls AutoDJ fade/skip
- Shift + play triggers stutter play
- Internal refactoring of hotcues
- Delete obsolete constants & triggers
- Minor changes
DN-MC6000MK2: Many MIDI mapping fixes

- Many MIDI mapping fixes, mainly for [Channel3/4]
- AutoDJ changes
  - Shift + Cue triggers skip_next
  - Shift + Play triggers fade_now
- Internal refactorings & cleanup
DN-MC6000MK2: Only 4+4 samplers (shared between decks)

- MIDI debugging revealed that the sampler controls
  buttons/LEDs are sending/receiving on MIDI Ch0 (left side)
  and MIDI Ch2 (right side) independent of the currently
  selected deck.
- Automatically load selected track into empty deck
  or sampler when pressing the cue/play or the sampler
  button respectively
DN-MC6000MK2: Sampler modesSampler modes + crossfader configuration

- Support 2 different sampler modes:
  - Hold (the new default)
  - Trigger
  The default sampler mode can be changed by setting DenonMC6000MK2.DEFAULT_SAMPLER_MODE appropriately.
- Assignment of crossfader to channels
- Modify contour of crossfader curve
- Delete unused booth level control