Return 1plenary for area of plenaries to get closer to the behaviour

of the old models, fixes problem with plenaries only being visible in
the week view if GEN is selected.
 - Legacy-Id: 4083

ietf/meeting/proxy.py

@@ -442,7 +442,9 @@ class WgMeetingSessionProxy(TimeSlot):
         if not self.session or not self.session.group:
             return ""
         if self.session.group.type_id == "irtf":
-            return "irtf" 
+            return "irtf"
+        if self.type_id == "plenary":
+            return "1plenary"
         if not self.session.group.parent or not self.session.group.parent.type_id in ["area","irtf"]:
             return ""
         return self.session.group.parent.acronym