Test click and keyboard behaviours explicitly

[rafaqz]

We need tests for all clicks and key commands with PaintCanvas and GeometryCanvas.

Clicks and key presses can be simulated with:

event.keyboard[] = value 
scene.events.mousebutton[] = ... 

I'm imagining things like clicking in the PaintCanvas and checking the matrix values are correct, and clicking in Point/LineString/Polygon GeometryCanvas with the various key commands and checking the geometry vectors have the right contents.

See #14