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.

Only import from github when changes are made, rather than exporting. Th...

Conflicts:
	lms/urls.py

* move html_checker.py
* move stringify.py
* move tests into module
* remove duplicate progress.py
* fix module imports

* cleaned up error module:
  - only one template
  - save error message in xml and reload
* better display of problem definition and metadata to staff
* save error messages as string, not exception objects.

Feature/victor/metadata inherit