Restricting the receipt API to authenticated users (bug 917601)

Otherwise a 500 will be raised given the usage of `request.amo_user`
add italian (bug 918560)
document ?region in search API (bug 917500)
fix field names in search.rst
Don't apply filters to Collections API when pk/slug/etc lookup is used (bug 915801)
Merge pull request #1163 from diox/collections-dont-filter-lookups

Don't apply filters to Collections API when pk/slug/etc lookup is used (bug 915801)
Commit from Mozilla Verbatim by user petercpg@mail.moztw.org.: 5047 of 5474 strings translated (0 fuzzy).
Merge branch 'master' of ssh://github.com/mozilla/zamboni
Commit from Mozilla Verbatim by user mdinic@mozilla.com.: 406 of 5474 strings translated (2 fuzzy).
remove paypal check
Expose fallback used  in Collections API (bug 914318)
Merge pull request #1165 from diox/collections-expose-fallback

Expose fallback used  in Collections API (bug 914318)
Commit from Mozilla Verbatim by user petercpg@mail.moztw.org.: 5086 of 5474 strings translated (0 fuzzy).
Merge branch 'master' of ssh://github.com/mozilla/zamboni
Commit from Mozilla Verbatim by user petercpg@mail.moztw.org.: 5087 of 5474 strings translated (0 fuzzy).
Commit from Mozilla Verbatim by user petercpg@mail.moztw.org.: 5087 of 5474 strings translated (0 fuzzy).
Removed unused tasks.

See commit af6e6a7896cd9e5aa51d017f2abace084938669e.
check for image presence without database hit (bug 918522)
pyflakes cleanup
don't run files languagepack tests twice