Anonymous access to check transaction (bug 956354)

Third party apps need to hit the API to check fulfillment
of a hosted in-app payment.
fix feedapp images by namespacing the view (feed)
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)