Some cleanup of Stage3DProxy class.
Small comment typo fix in Stage3DProxy.
Made Stage3DManager.removeStage3DProxy() internal.
Added requestContext3D() method to Stage3DProxy. Needs to be called,
instead of automatically requesting the context but is more flexible in
the engine architecture.
Changed Render2D to accept an instantiated root view instead of a
root class which is more flexible in the engine context.

Adapted test classes.
Made changes to Render2D class to accomodate View2D as the root view.
Undo small change in FragmentFilter2D.