Made twirl effect a lot more beautiful.

include/effect_twirl.h

@@ -7,8 +7,9 @@
 class TwirlEffect : public Effect {
 private:
     uint8_t angleOffset = 0;
-    double center_x = 8;
-    double center_y = 8;
+    uint8_t _center_offset_angle = 0;
+    double _real_center_x = LED_WIDTH / 2;
+    double _real_center_y = LED_HEIGHT / 2;
 public:
     void loop();
 };