Make use of django_main for password_reset templates

Remove duplicated code and make sure those views use the same visual identity.
@singingwolfboy the `data-remote` attribute is used by `lms/static/js/form.ext.js`, this file is part of the `'application'` pipeline bundle.
That bundle was not included in this file, although it is in `main_django.html`.

This markup was probably copy/pasted from somewhere else.