Added is_ephemeral: a flag that determines if a model is automatically deleted when its related models are deleted
diff --git a/planetstack/core/models/plcorebase.py b/planetstack/core/models/plcorebase.py
index e483a79..782737c 100644
--- a/planetstack/core/models/plcorebase.py
+++ b/planetstack/core/models/plcorebase.py
@@ -201,6 +201,10 @@
         # filtering of visible objects by user.
         return cls.objects.all()
 
+    @classmethod
+    def is_ephemeral(cls):
+	return False
+