Made PageRef an actual reference

Signed-off-by: Wilson Brenna <wbrenna@uwaterloo.ca>
Fixed two off-by-one errors

Signed-off-by: Wilson Brenna <wbrenna@uwaterloo.ca>
Changed event handling

The UndoActions now fire events whenever content changes.
The PageViews receive the events and rerender themselves.

Signed-off-by: Wilson Brenna <wbrenna@uwaterloo.ca>
Fixed Stroke error.
Fixes redraw bug on firePageChanged.