fix bug 1029071 - send translated welcome emails

use pofile to check for translated strings

tests for default, translated, and untranslated

add trans blocks to HTML email
use vendor w/ polib; update vendor docs
add locale.tar.gz for travis
cleanups from #2532
fix db/celery race condition
task tests
Merge pull request #2569 from groovecoder/allauth-welcome-emails-1029071

fix bug 1029071 - translated welcome emails