Allow multiple SQL authenticators to be used without conflict.

Rather than clobber the user_model class variable every time a SQL
authenticator is used, use a hash to map auth_index to the associated
user model.
Fix translations.
Merge pull request #223 from pawurb/fix_translation

Fix translations.
Merge pull request #219 from davexunit/fix-sql-authenticator

Allow multiple SQL authenticators to be used without conflict.
Fix error: undefined local variable or method `user_model' for CASServer::Authenticators::SQLEncrypted:Class (NameError)
Merge pull request #224 from korun/master

Fix error: undefined local variable or method `user_model' for CASServer...