Deleted the node_categories addon. This was broken for some time now and would need to be rewritten from scratch anyway.

There is now a shiny new node categories system in trunk (see custom_nodes.py template or release/scripts/startup/nodeitems_builtins.py for basic usage). This system could be extended in a new py addon
to provide the functionality of this addon in a nicer way.

git-svn-id: https://svn.blender.org/svnroot/bf-extensions/contrib@4558 96b784f8-4ae3-dd11-aff7-0030488c597c