Logistration: enrollment cleanup and a few fixes

Changes:

* Move redirection/enrollment to AccessView and trigger it using an event.
* Ensure window.isExternal is loaded
* Don't set a default for terms of service (this was causing registration to fail with the default sandbox config)
* For paid courses, add the course to the cart and redirect to the shopping cart view.

Reviewers: @rlucioni @AlasdairSwan 
FYI: @dianakhuang 
Sweet, didn't realize you could do that.  Updated it here and in "enrollment.js"