Make saving also save the children in the #sortable element (TODO: name the #sortable element better)

* New format: {tag}://{org}/{course}/{category}/{name}[@{revision}]
* Updated tests, code
* Added test chapter with : in url_name in toy course
* added test html page with : in url_name
* added a note to docs

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

Only import from github when changes are made, rather than exporting. This prevents bugs in the cms from preventing changes via git

* change custom tags in test/data/full to new single-tag format
* fix broken file references
* fix argument to import_from_xml
* error_handler fix in mongo.py in next commit

Add tests for the edit page for the toy course, and make sure that exporting to github sets up the git repo properly

* add optional author_str param to export_to_github
* pass the django user info to that param

* NOTE: successfully running the tests depends on an updated version of
  django-pipeline, which fixes a unicode bug (https://github.com/MITx/django-pipeline/commit/efaba4ac63bc635da6a728603e87e14758541ec7)

Config changes:
* Use separate db for the cms
* Run collectstatic before running tests--needed to get everything in the right place for loading pages
* fix some paths related to this
* Turn off JS compressor for CMS
* add empty test_root/uploads dir

Code changes:
* Add cms tests to check that home page and signup pages load
* Add cms account creation test
* Make github sync tests clean out repo dirs before running.