Better touch controls, stability and sprite pane scrolling

[foxnne]

Adds lots of better functionality to the main workspace areas and sprite pane:

• Momentum added to click + drag scrolling in sprite pane
• Momentum and functionality added to single touch/click drag to pan in empty area of workspace
• Sprites drawn in the sprite pane refined to better reflect selection state
  • If more than 1 sprite is selected, endlessly loop just the selected sprites
  • If 1 or less sprites are selected, but an animation is selected, loop the animation and scroll the current sprite
  • If nothing is selected, scroll the entire grid
• Pinch to zoom refined, before shadow and controls didn't match image zoom state
• press/click and hold on an empty space in the workspace to open tools radial menu, this should make touch controls much better
• Sampling empty space outside of drawable canvas switches to pointer tool, convenient