Use ugettext everywhere. Advances BiscuIT-ng#38.

biscuit/apps/untis/apps.py

 from django.apps import AppConfig
-from django.utils.translation import gettext_lazy as _
+from django.utils.translation import ugettext_lazy as _
 
 
 class UntisConfig(AppConfig):

biscuit/apps/untis/forms.py

 from django import forms
-from django.utils.translation import gettext_lazy as _
+from django.utils.translation import ugettext_lazy as _
 
 
 class UntisUploadForm(forms.Form):

biscuit/apps/untis/management/commands/untis_import.py

 from django.core.management.base import BaseCommand
-from django.utils.translation import gettext as _
+from django.utils.translation import ugettext as _
 
 from ...util import untis_import_xml
 

biscuit/apps/untis/menus.py

-from django.utils.translation import gettext as _
+from django.utils.translation import ugettext as _
 
 MENUS = {
     'NAV_MENU_CORE': [