Fix ugettext usage for transation: model fields should be translated lazily

panorama/models.py

@@ -11,7 +11,7 @@ from django.core.exceptions import ValidationError
 from django.core.validators import MinValueValidator, MaxValueValidator
 from django.core.urlresolvers import reverse
 from django.utils.encoding import python_2_unicode_compatible
-from django.utils.translation import ugettext as _
+from django.utils.translation import ugettext_lazy as _
 
 from .tasks import generate_tiles
 from .utils import makedirs, path_exists