Add class-based views to replace the built in  views.

A few notes.

- This is currently entirely untested
- There are a few differences in the kwargs between these views and the `django.contrib.auth.views` versions.
    - `authentication_form => form_class`
    - `password_reset_form => form_class`
    - `post_reset_redirect => success_url`
- The `login` view accepts a new parameter `disallow_authenticated` which defaults to `True`.  If true, authenticated users who visit the login view will be automatically redirected to the `success_url`.
- The `password_reset` view is responsible for sending the password reset email.  To override the default behavior which was copied in from `django.contrib.auth.forms.PasswordResetForm`, subclass `authuser.views.PasswordResetView` and override the `send_password_reset_email` method.  This method takes the `user` as the sole argument.