Remove pystache in favor of our custom version

ensuring pystache>=0.5.2

updating dependencies for pystache, networkx, graphviz and removing redu...

updating dependencies for pystache, networkx, graphviz and removing redundant dependency for django-staticfiles

- use get_instance, not get_item
- finish the id->location rename for modx_dispatch arg

Made save buttons blue, finished remaining askbot bugs, and removed all instances of $mit-red

Kimth/textbook

Keep each course's descriptors separate

Bridger/feature/clean up

moving all requirements that use a repo to repo-requirements.txt includi...

Feature/kfiedler/courseware style

* apply policy per-course, even if multiple courses share course and org fields
* keep descriptors separate in xml store, so that if two such courses
  change the same module in different ways, it works.  Such edits will need to
  merged on CMS import...
* add get_instance(course_id, location) method to replace get_item(location).
  Update all the call sites
* tests, including a 2nd toy course with same course and org.

Kimth/multiple fileupload

Fix broken dependency updates for wiki

Feature/bridger/new wiki