Import translations from Transifex for Juno

* Import ~100% completed translations
  (translations available for 12 languages)
* Update language list in openstack_dashboard settings.py
* Update English POT files
* Update Transifex resource name in .tx/config for Juno.
* Remove compiled message catalogs (Related-Bug: #1196982)

Closes-Bug: #1376542

The instruction on how to compile message catalogs will be
covered by https://review.openstack.org/#/c/126169/
or the installation guide.

Change-Id: Ib36562168009fa34b9818e99154df350678abd4b