Wiki pages can now be viewed from the course URL and the course nav is shown. It doesn't follow the user yet.

Created copy of main.html that is django template. Using this for wiki instead of converting every view.

* if the course metadata have enrollment_start and/or enrollment_end,
  only allow normal users to enroll post start and pre end.
* If DARK_LAUNCH is on, staff can enroll outside the window

* 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.

* Just log a warning and return a dummy url
* May want smarter checking later
  (e.g. would be nice to tell staff what files are missing.)

window, add xqa modal window, add xqa_key to course metadata

html is in a veritical)

* bodyclass block got accidentally deleted

* need to actually return 404 codes to clients when DEBUG=False
* add option to make nose more verbose and drop to pdb on error