upgrade to django-browserid 0.9

NOTE! django-browserid has changed a lot since 0.7.
See https://github.com/mozilla/django-browserid/blob/master/CHANGELOG.rst
The significant changes are:

 * SITE_URL is now only needed when DEBUG == False
 * SITE_URL can be a list of strings
 * Default CSS is available for pretty login and logout buttons
 * Replaced `browserid_button` with `browserid_login` and `browserid_logout,
   and made `browserid_info` a function
 * `LOGIN_REDIRECT_URL`, `LOGIN_REDIRECT_URL_FAILURE` and
   `LOGOUT_REDIRECT_URL` can no longer be named views. They have to be
   actual strings to redirect to.
 * Instead of adding `'django_browserid.context_processors.browserid_form'`
   to `TEMPLATE_CONTEXT_PROCESSORS` you need to add
   `'django_browserid.context_processors.browserid'`
   and instead of including `{{ browserid_form.media }}` use
   `{% browserid_js %}` (or `{{ browserid_js() }}` if you use jinja)
 * The JavaScript assumes you have jQuery 1.7 or higher