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
DN-MC6000MK2: Filters and initial effects support

- Effect units (ordered according to physical controller layout
  from left to right):
   - EffectUnit1: Left FX1
   - EffectUnit2: Left Filter
   - EffectUnit3: Right Filter
  - EffectUnit4: Right FX2
- Filters are fully functional
- FX1 and FX2 can be assigned to decks
- Minor changes of VuMeter sensitivity
DN-MC6000MK2: Basic effect chain control

- Effect chain selector (need to press shift as labeled)
- Efx3 button enables/disables the effect chain
- Efx3 knob for dry/wet control
- Efx2 knob for master parameter control ("metaknob")
- Minor cleanup
DN-MC6000MK2: Minor cleanup
DN-MC6000MK2: Scripting and effects refactoring
DN-MC6000MK2: Simplify sync logic

- Control sync mainly through "sync_enabled" instead of trying to
  select a specific "sync_mode". Mixxx already handles this
  internally and we should not override it here.
- Generalize shift button handling for easier switching between local
  and global Shift button handling
- Minor cleanup
Improving CoverArtDelegate::paint() - remove unnecessary QStyleOptionViewItem copy
Improving CoverArtDelegate::paint() - using trackmodel as a member to get it just once
Improving CoverArtDelegate::paint() - using defaultCoverLocation as a member to get it just once from CoverCache
Reintroduced tooltips for EQ preferences
fix restoring Bessel4 EQ at reset to default
Improving CoverArtDelegate::paint()

- getting coverLocation and md5 column just once;
- ordering calls in a better way;
After some analysis with valgrind, I noticed that fieldIndex() takes a long time and that we could call it just once (in the construction).
CoverArtCache - checking if the cover found is different from the cover that is already stored in db
- it avoids calling 'updates' when there is nothing to update...
CoverArtDAO - add method to save multi cover arts at once (from qlist)