Use tower-cell icon for cluster/unknown spots rather than the desktop icon

data/spot.py

@@ -300,6 +300,10 @@ class Spot:
         if self.sig:
             self.icon = get_icon_for_sig(self.sig)
 
+        # Default "radio" icon if nothing else has set it
+        if not self.icon:
+            self.icon = "tower-cell"
+
         # DX Grid to lat/lon and vice versa in case one is missing
         if self.dx_grid and not self.dx_latitude:
             ll = locator_to_latlong(self.dx_grid)
@@ -380,7 +384,7 @@ class Spot:
         self_copy.received_time_iso = ""
         self.id = hashlib.sha256(str(self_copy).encode("utf-8")).hexdigest()
 
-    # JSON serialise
+    # JSON sspoterialise
     def to_json(self):
         return json.dumps(self, default=lambda o: o.__dict__, sort_keys=True)