Url resolvers for angular controllers

A pull request to discuss new url reversers. 

* What to do with old code (urls by namespace to angular constant)?
* Renaming (according to the survey)?
Yes, I copied the text from ``manage-urls.rst``. And I guess it should be replaced eventually, since both are about the same functionality, but we should also retain backwards compatibility, both by keeping the ´´urls_by_namespace´´ code and the "old" docs, but mark it as deprecated.

Anyway that's one of the issues that have to be addressed before merging.