* Uses override_settings to provide test variable
* Move location of cms link to upper right
* PEP8 / Pylink

A one-click way of getting to editing the course

Authors can upload an image (or choose an existing one) from the
settings page, using the in-context uploader from PDF
textbooks. Includes tests for backwards compatibility with XML courses
-- they used a magic filename (images/course_image.jpg) which is
mapped to a location in the Mongo contentstore.

Still needs some UX work, though the backend plumbing is there.

fix (again) static_replace to work with static_asset_path

WIP: added a get_modulestore_type. Added some unit tests. changed over the isinstance() with respect to modulestores to use this get_modulestore_type()

This makes the LMS use an XBlock's student_view, rather than an
XModule's get_html to render for display. However, it does not yet use
wrap_child to handle instructor debug information or url rewriting.

[LMS-219]

This reverts commit c4f56620.

This reverts commit ab437b94, reversing
changes made to 7a8e87c7.

- Create new cohorts.py file
- moved code there from models.py
- implemented necessary functions.

Next: testing :)

fix cohorts in create, and read, and update regular expressions to fix courses with periods not working in General commentable

If there is no announcement date (in the policy metadata) then use a
heuristic to sort them.

If there is an announcement date, the use it in the heuristic to
determine if the course is new or not.

The property can be set in the policy metadata. If it is not specified
then it is set to true if the course has not started yet.

Also adds a property to check how many days are left until the course starts.

This cuts the number of queries in 6.002 courseware loads from ~650 to
~5-40. Still to do: cache CustomTag templates so that we only load them
once per request.