Can set scraperwiki scraper to fork by shortname in model
Don't set scraperwiki_url if setting scraperwiki_shortname to nil
Can pass the scraperwiki shortname to the form for forking from scraperwiki
Update instructions to include python support
Now will correctly return to authenticated page after logging in
When signing out return to the home page

Doing this because if you are on an authenticated page and you log in and you
stay on the same page (as was the previous behaviour) then it asks you to log
in again which is kind of weird.