Anonymous access to check transaction (bug 956354)

Third party apps need to hit the API to check fulfillment
of a hosted in-app payment.
make feedapp attribution a plain charfield (feed)
Removed custom code and a TODO
allow PUT on feed api (feed)
Remove leftover AMO views, templates, template tags (bug 973140)
Merge pull request #2112 from diox/remove-amo-views

Remove leftover AMO views, templates, template tags (bug 973140)
update feed app 'image' to 'background_image'
Merge pull request #2114 from kumar303/fxpay-status

Anonymous access to check transaction (bug 956354)
Process postback for anon. purchase (bug 1019269)

This supports server-less in-app payments.
Merge pull request #2115 from kumar303/fxpay-postback

Process postback for anonymous purchase
rename image to background_image for feedapp (feed)
clean up stale custom sql
Pull in elasticutils with django to pick up settings
Creates new base Collection model for feed-related collection, implements it on editorial brand model