Add I18N related configurations

* Add Transifex config
* Add babel config to setup.cfg (extract_messages, compile_catalog)
* Add Babel to test-requirements.txt (It is only required
  when extracting and compiling catalogs
* Move English PO file to openstack_auth.pot
  (following other OpenStack projects)
* Remove English MO file

Change-Id: I7a908006c7a2c586d9d86cbfe3970b56f1461125
Merge "Add I18N related configurations"