Integrate "migration" page to IPA Web framework.
    
    To use all advantages of entire Web framework the "migration" page
    should use "migrate" plugin. As well this allows to use IPA
    translations.
    
    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>