Fix for frame node property display: Extended frame node properties such as the "shrink" option were not shown in the node editor sidebar. This was because the RNA type for the node was not using
NodeInternal as a base, which is a wrapper to expose the C callbacks as methods in bpy. Now these basic node types are also based on NodeInternal to ensure the full interface is available to py scripts.

In the process removed the unused NodeGroup register function, this doesn't work nicely anyway because it requires multiple inheritance which RNA doesn't support (so py node groups should be done
entirely in python in the future).

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57258 954f8c5b-7b00-dc11-b283-0030488c597c