Split out code to replace /static urls in get_html into a separate module so that it can be used in CMS previews

Django hardcodes the subject line for password reset emails. You're supposed
to be able to override it with a properly named template, but that didn't
make it into 1.3.1 (which is what we're deploying on now). We're not using
the Sites framework at this time, so this was the "fix".

Requires the replacement of {COURSE_STATIC_URL} with just /static/
in about/overview.html files.

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.

Registering now temporarily logs you in. A message is displayed on the dashboard, reminding you to activate your account. Logging in shows a reminder about activating.

* Changed from 'male', 'female', and 'other' to 'm', 'f', and 'o'