* specify in tabs list in course policy
  - active page tracking now done in tabs.py
  - properly handle the fact that there may be multiple textbooks

* Still need:
  - wiki pages
  - (if that's delayed, special-case syllabus support)

- don't call has_access directly from template, pass a staff_access variable instead

* All access control logic is now in access.py
* It exports a single method for general use: has_access(user, object, action)
 - possible actions depend on object type (e.g. 'see_exists', 'enroll', 'staff')
* Removed DARK_LAUNCH feature flag--it is now the default behavior
* Replaced check_course with three separate more focused functions that use has_access

Minor things:
* note on using pdb in testing
* moved time parsing helper into timeparse.py
* x_modules now have a .start attribute (None if not in metadata)

* pass user to check_course
* if dark launch feature enabled, users with staff access to course
can see courseware before start date.  Students still can't.
* tests.
* Remaining: enrollment view has custom access control.  Need to check it.

Changed check_course from a decorator to a regular function that throws exceptions. Much easier to understand now.

The basic form has been fleshed out. Things still to do:
1) Extend get_course interface to the rest of modulestore
2) Make courses actually load
3) Make org/course/maybe others metadata attributes for course_module (see xml_module), so
that they are loaded/saved on import/export to xml