Display brightness support (#26)

* cleanup

* brightness control and app

* cleanup

* persistant storage of display settings

* fix for missing include

* header cleanup

* fix pc build

* add docs

* move display app to tactility project

boards/lilygo_tdeck/lilygo_tdeck.c

@@ -1,4 +1,5 @@
 #include "lilygo_tdeck.h"
+#include "display_i.h"
 #include <stdbool.h>
 
 bool tdeck_bootstrap();
@@ -8,6 +9,9 @@ extern const SdCard tdeck_sdcard;
 
 const HardwareConfig lilygo_tdeck = {
     .bootstrap = &tdeck_bootstrap,
+    .display = {
+        .set_backlight_duty = &tdeck_backlight_set
+    },
     .init_lvgl = &tdeck_init_lvgl,
     .sdcard = &tdeck_sdcard
 };