windows: use a better systray default icon

Draw a blue circle as default icon in the systray. Use the same
blue color as the one shown in ogCP for an ogClient Windows instance.

src/windows/ogOperations.py

@@ -23,20 +23,23 @@ from src.ogRest import ThreadState
 def _create_default_image():
     """
     Creates a default image for the tray icon. Use in case
-    no favicon.ico is found.
+    no favicon.ico is found. The image will be a blue circle.
     """
     width = height = 250
-    color1 = (255, 255, 255)
-    color2 = (255, 0, 255)
+    circle_color = (45, 158, 251)
 
-    image = Image.new('RGB', (width, height), color1)
+    # Create a new image with a transparent background
+    image = Image.new('RGBA', (width, height), (0, 0, 0, 0))
     dc = ImageDraw.Draw(image)
-    dc.rectangle(
-        (width // 2, 0, width, height // 2),
-        fill=color2)
-    dc.rectangle(
-        (0, height // 2, width // 2, height),
-        fill=color2)
+
+    # Draw circle
+    circle_radius = min(width, height) // 2 - 10
+    circle_center = (width // 2, height // 2)
+    dc.ellipse(
+        (circle_center[0] - circle_radius, circle_center[1] - circle_radius,
+         circle_center[0] + circle_radius, circle_center[1] + circle_radius),
+        fill=circle_color
+    )
 
     return image