Fix various issues around setting up a new dev instance of the site.

- Add registration to JINGO_EXCLUDE_APPS to prevent admin logout
  template from being rendered by Jinja.

- Update signal for default permissions to abort if the
  can_share_website permission doesn't exist yet, which occurs when
  creating an admin during the initial syncdb. Also adds tests for this
  signal.

- Update install docs to have correct paths.

- Remove FacebookDebugMiddleware; Facebook app testing can be done with
  a test app, and it causes import issues.
Remove django-browserid submodule.
Install latest django-browserid.
Configure site for django-browserid, add placeholder login button.