Pulling out r42105 for now -- "Added 2 hooks. One in Parser to allow custom handling...

Pulling out r42105 for now -- "Added 2 hooks. One in Parser to allow custom handling of namespace links, and one in EditPage, to allow custom output/handling when a user has no edit rights"
The namespace parsing thing feels very hacky and grabs bits out of an internal implementation function which doesn't feel like a stable interface.
Would recommend thinking about this and coming up with a more serious stable interface for it.