I'll go ahead and merge this, since it fixes nearly all the issues we had with problem and html css, and this should go in before more changes. The table borders can be fixed in another round.
* 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.
* 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
* Refactor index() so that it makes sense to me and hopefully others :)
* Rename preloaded cache of student modules to student_module_cache
* Fix line length and whitespace throughout
* add docstrings and other comments
* a few behavior-preserving tweaks to the code to make it clearer.
* Separate codepaths for with-module and without-module in index view
* Remove default chapter + section, since they don't exist anyway in course.xml
