expose whether we're transitioning state

tangostationcontrol/tangostationcontrol/devices/station_manager.py

@@ -76,6 +76,10 @@ class StationManager(AsyncDevice):
     def station_state_R(self):
         return self.station_state.name
 
+    @attribute(dtype=bool, fisallowed="is_attribute_access_allowed")
+    def station_state_transitioning_R(self):
+        return self.transition_lock and self.transition_lock.locked()
+
     @attribute(dtype=str, fisallowed="is_attribute_access_allowed")
     def last_requested_transition_R(self):
         return self.last_requested_transition or ""