GWTII-134: clearRect() as some browsers don't clear on resize
GWTII-134: javadoc
Merge branch 'GWTII-134_CanvasRenderer' of
github.com:geomajas/geomajas-project-client-gwt2 into
GWTII-134_CanvasRenderer

Conflicts:
	impl/src/main/java/org/geomajas/gwt2/client/map/render/canvas/container/CanvasTileGrid.java