Improve import from Locamotion

With the current code, we're importing only untranslated strings, and I think it's bad since we're basically not letting these locale do QA.

Changes:
* when importing strings, add {ok} if translation == id (based on https://bugzilla.mozilla.org/show_bug.cgi?id=883903#c10)
* import all changed strings from Pootle

A couple of tests on cy and xh
http://viewvc.svn.mozilla.org/vc?revision=124842&view=revision
http://viewvc.svn.mozilla.org/vc?revision=124843&view=revision