audio/din: Update to 55

Changes since 54:

DIN Is Noise 55:
  /*
      an overhaul of Gravity

      as before, you can click and move the base or
      the tip of the gravity arrow to adjust its position,
      direction and strength.

      to (auto) animate the gravity arrow:

        assign a drone to base of gravity
        assign another drone to tip of gravity

        move or visual FM / AM modulate one or both these drones
        and gravity moves accordingly.

        animating gravity influences the trajectory of launched
        drones :)

      click 'Base to manual' and 'Tip to manual' to detach
      assigned drones from base and the tip respectively.

      you can now manually edit the base and tip again.

      click 'Select base', 'Select tip' or 'Select both'
      to select the assigned drones. Useful for moving,
      for visual AM/FM, to mute them etc.

      eg., you could mute the assigned drones by clicking
      'Select both' and then Menu > Drone Tools > Mute

  /*

  /* adjust position/phase of visual drone modulation (AM and FM)

      Menu > Drone Params > AM Position
      Menu > Drone Params > FM Position

      eg., at 0 position with AM and FM BPMs equal, the trail/path
      of the modulating drones is elliptical.

  /* set AM BPM to FM BPM of drones and vice-versa
  /* flip velocity direction of launched drone with respect to the launcher
     if -ve flag is set in drone velocity defaults
  /* opacity parameter for oscilloscope
  * optimised oscilloscope
    * faster sample add
    * faster drawing
  * changed shape of drone handles
  * optimised snap lines drawing on curve editors
  ! fixed OpenGL drawing bugs for affected OpenGL drivers on Windows !
    ! in oscilloscope !
    ! in waveform display on waveform editors !
    ! when hz/vol displayed on drones !
  ! fixed crash if drones as they are fading in when creating drone mesh
    are modulated or moved !