Attempt to fix CPU utilisation bug by preventing the heartbeat callback leak in the SSE stream handlers and replacing Timer-based with Event-based threads. Also compiled regexes in advance for DXCC callsign lookups for efficiency, and fixed my misunderstanding of what Queue.empty() does

core/utils.py

@@ -3,3 +3,12 @@
 # to receive spots without complex handling.
 def serialize_everything(obj):
     return obj.__dict__
+
+
+# Empty a queue
+def empty_queue(q):
+    while not q.empty():
+        try:
+            q.get_nowait()
+        except:
+            break