refactor app code (#93)

AppSim/Source/HelloWorld/hello_world.cpp

@@ -1,6 +1,6 @@
 #include "lvgl/Toolbar.h"
 
-static void app_show(tt::app::App app, lv_obj_t* parent) {
+static void app_show(tt::app::App& app, lv_obj_t* parent) {
     lv_obj_t* toolbar = tt::lvgl::toolbar_create(parent, app);
     lv_obj_align(toolbar, LV_ALIGN_TOP_MID, 0, 0);
 
@@ -13,5 +13,5 @@ extern const tt::app::Manifest hello_world_app = {
     .id = "HelloWorld",
     .name = "Hello World",
     .type = tt::app::TypeUser,
-    .on_show = &app_show
+    .onShow = &app_show
 };