Adding data_change to use to signal to Screenful that save button nedds a litle star

src/update.py

@@ -1,3 +1,5 @@
+import lib.screenful as screenful
+
 class Update:
     def __init__(self):
         self.message_queue = []
@@ -10,6 +12,10 @@ class Update:
             if msg.reset():
                 self.model.reset()
                 break
+            
+        for msg in self.message_queue:
+            if msg.data_change():
+                screenful.changed()
         
         for msg in self.message_queue:
             msg.update_model(self.model)