Add Django apps for student account and profile

Add Python APIs for account/profile information to user_api
Updating profile page to have social linking

@stephensanchez @rlucioni @AlasdairSwan Please look over these changes.  Since this is behind a feature flag, we don't need this to be 100% complete, but the functionality we've implemented so far should work correctly.
Yes.  I believe this is the current behavior of the system.  Alternatively we could filter on `is_active` here, but then there's the potential that:

1) Someone registers as "foo@example.com"
2) I request to change my email to "foo@example.com"
3) The other person activates their account
4) I get an error when I try to confirm the change.