Revert "Revert "Don't use Horde_Auth::factory""

This reverts commit 4e774e93c21d3a5a9cf767c6d6ff2c4de467ee43.

Forgot to commit the _getDriverName() part.
Use _getDriverName() to get proper classname
gettext_define() -> r()
Add r() ability to application code, and document in TRANSLATIONS