Bring back sites app, since it is referenced from comments app

Add a fixture for site: vlevit.org
Add manage.py authorize_gplus command

Google+ authorization is done from the command line and credentials are
saved to json file. User intervention is needed only once. After
refresh_token is retreived, access tokens can be updated automatically.

Later this will used to export blog entries to G+.
Update server requirements
Add Google+ redirect view