Cosmetic fixes on references services and user form.

taiga/projects/references/services.py

@@ -1,9 +1,11 @@
-from .models import Reference
+from django.db.models.loading import get_model
+
 
 def get_instance_by_ref(project_id, obj_ref):
+    model_cls = get_model("references", "Reference")
     try:
-        instance = Reference.objects.get(project_id=project_id, ref=obj_ref)
-    except Reference.DoesNotExist:
+        instance = model_cls.objects.get(project_id=project_id, ref=obj_ref)
+    except model_cls.DoesNotExist:
         instance = None
 
     return instance

taiga/users/forms.py

@@ -15,10 +15,10 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 from django import forms
-from django.contrib.auth.forms import (
-    UserCreationForm as DjangoUserCreationForm,
-    UserChangeForm as DjangoUserChangeForm
-)
+from django.contrib.auth.forms import UserCreationForm as DjangoUserCreationForm
+from django.contrib.auth.forms import UserChangeForm as DjangoUserChangeForm
+
+
 from .models import User