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

- Add no extras to the banner admin BannerImageInline. Any blank extras
  cause the entire form to fail to submit.

- 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.

- Use Pillow instead of PIL in requirements files; PIL has a hard time
  finding JPEG support on developer machines, whereas Pillow makes
  everything better. Servers can still use PIL if they wish.

- Remove FacebookDebugMiddleware; Facebook app testing can be done with
  a test app, and it causes import issues.