Move state changes away from render method to refresh method

Backwards compatibility is preserved by calling refresh for each node at
the beginning of rendering. This is performed automatically in
G2DSceneGraph.render contrary to original requirement. This change is
required to support external diagram renderers.

Change-Id: I5d91ee97b0c9527f6d4ba562089ffaebdbc01ce0
(cherry picked from commit 512d469c3e490cdfc9a10fbbd6efe92ae6c0358a)