Updated changes.txt.
Renamed ScreenView.LAYOUT_BOUNDS to DEFAULT_LAYOUT_BOUNDS, see https://github.com/phetsims/joist/issues/100
Transform fix for clearing the Canvas, see #22
Fixed what I think was a typo from a fix made previously.
Made the front cover of the book pickable, see #23.
Updated changes.txt.
Merged in some fixes made on the master branch.