Fix moved links

format should be
<ul>
<li>link</li>
<li>other link</li>
</ul>

missed instance of login link which should have been behind DISABLE_LOGIN_BUTTON

* 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)

Cleaned up activation pages. Added "Log In" link to notice when anonymous user tries to enroll in course.

If a user is anonymous when they click the enroll button, they will automatically be enrolled in the course if they immediately log in our create an account.

Added {COURSE_STATIC_URL} format key for about section html. Changed get_about_section to be get_course_about_section in courseware.courses.