Use lazy gettext in models and forms to allow things to be shown in Spanish.

apps/files/models.py

@@ -1,6 +1,6 @@
 from django.contrib.auth.models import User
 from django.db import models
-from django.utils.translation import ugettext as _
+from django.utils.translation import ugettext_lazy as _
 
 from apps.map.models import CaseStudy, CaseStudyDraft