Fix translations of messages in LoginScreen widget
To be translatable messages should be marked with '@i18n' and
present in "i18n_messages" dictionary.
Fixes: https://pagure.io/freeipa/issue/7619
Reviewed-By: Petr Vobornik <pvoborni@redhat.com>
Reviewed-By: Serhii Tsymbaliuk <stsymbal@redhat.com>