Add a label to costs app

costs/__init__.py

@@ -0,0 +1 @@
+default_app_config = 'costs.apps.CostsConfig'

costs/apps.py

@@ -0,0 +1,6 @@
+from django.apps import AppConfig
+
+
+class CostsConfig(AppConfig):
+    name = 'costs'
+    verbose_name = 'Coûts de revient'