Roundtrip HTML module editing working in the CMS

Victor/xml testing

TODO:
  - support picking a different course name
  - make it use current module rendering path, get that working.

* wasn't passing namespace properly in parse_course_file

* Separate out all xml processing code from django code
* Preparing to move the content parsing parts into common/lib/xmodule (?)

bugfix: lcp score can apparently be 0/0

Victor/show student state

* use clearer names for the two status strings passed to js
* add functions to do canonical conversion of progress to js string
* fix updating bug in sequence.coffee
* add some todo comments and other docs to make future expansion easier

* change bottom border of links:
  red for not started
  yellow for in_progress
  green for done

* This should probably be designed at some point.
* Obvious problems: the yellow is not very visible, and lots of people are
  red/green color-blind.

Fix render of lms index with no chapter or section.

modify capa_problem to add <include file="foo"> functionality

Victor/progress tracking

Fix accordion rendering bug

Switch cms over to django pipeline

Cleanup from https://github.com/MITx/mitx/pull/120

* add module_from_xml param to I4xSystem
* use it to implement xmodule.get_children()
* fix a few comments here and there
* Render-time progress display for seq and vertical modules.
  - Computes fraction of subproblems done.
* Pass problem state back to js during ajax calls.
* general cleanup in capa_module.py
* add progress_changed and progress fields to json returned from each ajax handler

* Coffeescript changes to hook up sequence tracking of problem progress

* net result: sequence 'a' tags now have a progress class
* properly set css class on initial load
* fire event when progress changes after ajax calls
* also save state in 'progress' property of problems-wrapper tag
* event handler finds those tags, computes updated progress