improved midi note editor + several fixes (merge for v2.0)

[raphaelquast]

❗ layer-switch buttons have changed (to simplify switching layers) ❗

• chan now activates the sequencer-layer (pressing chan again initializes a MIDI sequence)
• shift + chan activates mix-layer
• double-tapping shift now permanently activates the shift-layer

new

• activating the control-layer now automatically changes the Ableton-view to show the DeviceChain
• encoder 8 & 16 now work the same in ALL layers (use them to select tracks/scenes or scroll drumracks if shift is pressed)

🚀 major updates to the usability of the MIDI note editor (sequencer): Multi-Touch Editing!

❗ button & encoder assignments for the sequencer-layer have changed ❗

• tap a button to mute / unmute the corresponding note
• >> touch and hold << one or more buttons + turn the transpose-encoder
  to change the assigned property of the corresponding notes
  • set the "assigned property" (e.g. pitch, velocity, duration, . . . ) via encoder 1-6
  • set loop start/end and position via encoder 9-13
    • if no button is pressed, the transpose-encoder now changes the "assigned property" for ALL notes
• similarly encoder 15 now sets the "assigned property" of all notes inside the loop
  • ... finally you can also use shift + encoder 1-16 to set the "assigned property" of notes 1-16 directly

fixes

• deletion of return-tracks now works as expected (control)
• "load item on new track" no longer creates unnecessary return-tracks (browser)
• fix error for duplication of clips in the last scene (shift)
• properly check start < end condition before setting loop (sequencer)
• important status-bar messages now remain visible until the layer is deactivated
• indicate empty group-slots as "magenta" (and "blue" if clips are present inside the group) (launch)
• better color-indication of the activated layers