Remove Accept-Language fallback in RegionMiddleware (bug 941939)

It does us more harm than good, I shouldn't be localized in the US
just because I have en-US as my prefered language.
Alter editors.tests.test_models to make them more robust

They previously passed mostly by accident, because they were creating
Addons in an impossible state (public, with only non-public files).

Needed for django 1.6.
Remove some logging that is no longer necessary
Merge pull request #1758 from diox/remove-geoloc-language-fallback

Remove Accept-Language fallback in RegionMiddleware (bug 941939)
Fix tests that were relying on the Accept-Language region detection
Fix more tests that were relying on the Accept-Language region detection
Add labeled string format parameter (bug 972551)
Merge pull request #1761 from JaredKerim-Mozilla/972551

Add labeled string format parameter (bug 972551)
Added CORS headers to installed/mine api (bug 972484)