Merge pull request #856 from ngokevin/themestats

theme statistics (bug 565813)
Added caching around featured apps for API (bug 869715)
whitespace fix
Change receipt.txt to .html so localization picks it up (bug 865804)
reject too-large packaged app uploads early with 413. (bug 861516)
move a couple more things into fireplace/ (bug 875536)
move shared secret to authorization header (bug 870976)
nothing to see here
Cleaned up featured and categories (bug 869715)

* Removed a Category ORM query we didn't need.
* Brought consistency to what we passed to `featured`.
urllib2 header objects are never falsey
update polish date; bug 891124
update date; bug 891124
update date; bug 891124
Fixed featured with no category
Fix for test
Apples to apples so we search the right index (bug 891141)
Allow rejected files to be diffed on marketplace (bug 886274)
update list of waffles in waffle API
update theme check to return correct version (bug 880490)
hide categories only if the app is actually featured (bug 891140)