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?
I think a 400 is more appropriate here -- there's something wrong with the request, not an unexpected error on the server.

I also think these two cases are different enough that they should be separate test methods:
* `test_password_change_no_such_user`
* `test_password_change_inactive_user`