Light up LEDs on the display when switching layers

When switching layers, light up the appropriate LED on the display. For this
purpose, start led_display.[ch], which as a start, has a function to set the
brightness of a layer led.

The function will also turn all other LEDs off, and turn all of them off when on
the base layer.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>

right/src/led_display.h

@@ -0,0 +1,8 @@
+#ifndef __LED_DISPLAY_H__
+#define __LED_DISPLAY_H__
+
+    #include "led_driver.h"
+
+    void LedDisplay_SetLayerLed(uint8_t layerId, uint8_t brightness);
+
+#endif