[API,INTERNAL] Fix parameter order for graph and index property maps.

Also major cleanup of graph_property.h.
[API] Removing Raw Internal Maps for graphs.

Users can and should use the InternalMap<> wrapper for this.  The
generated code should be the same.  Anyway, I believe that nobody is
using this in the wild anyway.
[FEATURE] Cleaning up property maps.
[DOC] Improving property map API documentation.