Moved apps/addons/ to mkt/webapps/ (bug 1021189)

Note: I'm leaving addons/fixtures/ for now since other tests under apps/ may use them. Once we're done moving apps we theoretically can delete them all b/c we've updated the tests.
I know. :grin:  I was hoping when you cleaned up translations you could take care of this. These aren't going to get run until they're moved. :grimacing: