Calibration states (#820)

* color calibration

libs/core/buttons.ts

@@ -247,6 +247,15 @@ namespace brick {
     // the brick starts with the red color
     let currPattern: StatusLight = StatusLight.Off;
 
+    /**
+     * Gets the current light pattern.
+     */
+    //% weight=99 group="Buttons"
+    //% help=brick/status-light
+    export function statusLight() {
+        return currPattern;
+    }
+
     /**
      * Set lights.
      * @param pattern the lights pattern to use. eg: StatusLight.Orange