and modify course_navigation correspondingly

Feature/victor/use url names

External auth

* update templates and code references
* also a display_name property that defaults to cleaned url_name

* got rid of the hackish conversions between ' ' and '_'
* use url_name and display_name where appropriate
* update templates to match.

* CMS no longer syncs, it just imports when it gets a commit note
  from github

Feature/victor/xml verify

* may be temporary if we move errors into the items themselves.