Improve zooming

[akaDuality]

Closes #319

• Add big insets to free space for additional frames
• "Fit" button should place all frames in center of document
• Fix zooming by touchpad
  • Can zoom by pinch
  • Can double tap touchpad for smart zoom
    • Can show all frames if already zoomed on one of the frames
  • CMD-scroll should zoom by mouse
  • Can swipe by two fingers on touchpad (Also calls scrollWheel, but don't requires holden CMD

Fixed bugs

• Outline is not drawn during drag'n'drop
  • Refactor links to hud and drag'n'drop view at CanvasScrollView
• Samples window opens every launch
• Top and left inset are weird. Refactor as a result: not center, but add correct insets