Provide translatable messages for MigrateScreen widget
    
    Translatable messages should be marked with @i18n. Also
    these messages should be presented in "i18n_messages" dictionary.
    
    Fixes: https://pagure.io/freeipa/issue/7641
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Petr Vobornik <pvoborni@redhat.com>
    Reviewed-By: Serhii Tsymbaliuk <stsymbal@redhat.com>