Drawing improvements
* Adds proper pen position caluclations for Intuos small tablet
* Adds fake tilt when tablet doesn't support it or when using mouse
* Scales brush size with devicePixelRatio
Cleans up chunk and board selection
* Handles navigating chunks without throwing an error at beginning and end
* De-duplicates chunk and board selection code
* Cleans up some sketchpane calculations
Merge branch 'master' of https://github.com/setpixel/storyboard-fountain