Add MigrateScreen widget
    
    This widget is intended to integrate password migrate page into the
    entire IPA Web framework. The functionality is the same as mentioned
    standalone "ipa/migration/index.html".
    
    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>