Add password reset request handling to the account page

As per [ECOM-347](https://openedx.atlassian.net/browse/ECOM-347). The next step in the password reset process (confirmation) is currently handled by student.views.password_reset_confirm_wrapper, a custom wrapper around Django's password reset confirmation view.

@wedaly and @stephensanchez, could you review this?
Agreed. For the sake of consistency, if we're returning a 400 in this case, we should also return a 400 if an email change is requested for a user which does not exist. I'll update them both.