Added CMS_NODE_TYPE as descendant of CMS_CONTENT_TYPE,
in case we have content which is not a node in the future.
(probably useless, but for now, this extra abstraction is harmful)
Moved all node related code under node module cluster.
Applied comments from Javier Velilla.
Code cleaning.
but this is an example about on to add a new content type, and support it.
Fixed new node form workflow.
The current state is not final, it requires many changes, but for now, it implements a node editing workflow.
