Add graphics/ directory to .slugignore
Add ruby version to Gemfile
Try putting Gemfile* in .slugignore to stop Heroku thinking this is a Ruby app
Remove PIL module.

I don't *think* we're using it for anything...
Set ALLOWED_HOSTS in env vars for live and staging sites
Tweak os.environ import
Add Pillow (looks like we needed it or PIL after all)
Temporarily try setting PREPEND_WWW to False for staging
Get PREPEND_WWW setting from env on Heroku
Correctly deal with reading PREPEND_WWW from env