Make user profiles work again after the switch to an XMLModuleStore. Staff user histograms are still broken

Begin using a Keystore for XML parsing. Still broken: sequence icons, custom tags, problems, video js

Move the resources_fs abstraction into the primary DescriptorSystem, as it is needed for more than just XMLParsing

Remove semantically meaningless sections from course.xml by moving their attributes onto the contained element. If there is more than one contained element, turn the section into a sequence. Also handles includes

Also:
Render all XModuleDescriptors in the cms the same way
Default them to editing raw xml, if there is no specific module for them

* 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

Add categories and XModuleDescriptors for all module types that are used at the top level of a course

Refactor for reusability: x_modules take common parameters as an object. capa_problem to take a file object and not filename.

--HG--
branch : pmitros-mod-template

Semi-generic registration mechanism for modules. Still need to clean up references in content_parser

--HG--
branch : pmitros-mod-template

--HG--
rename : courseware/capa_module.py => courseware/modules/capa_module.py
rename : courseware/html_module.py => courseware/modules/html_module.py
rename : courseware/schematic_module.py => courseware/modules/schematic_module.py
rename : courseware/video_module.py => courseware/modules/video_module.py
rename : courseware/x_module.py => courseware/modules/x_module.py