control.py: Allow to stop blinking when timer runs out

Previously it wasn't able to be canceled.

Signed-off-by: Daniel Schaefer <dhs@frame.work>

Author: JohnAZoidberg

control.py

@@ -597,7 +597,11 @@ def countdown(seconds):
 def blinking():
     """Blink brightness high/off every second.
     Keeps currently displayed grid"""
+    global STOP_THREAD
     while True:
+        if STOP_THREAD:
+            STOP_THREAD = False
+            return
         brightness(0)
         time.sleep(0.5)
         brightness(200)