Enable buttons and the display.

Kind-of-sort-of usable-ish.

ButtonManager.h

@@ -21,6 +21,7 @@
 
 #pragma once
 
+#include <functional>
 #include "Task.h"
 #include "ReturnCode.h"
 
@@ -59,7 +60,7 @@ public:
          NOT_PRESSED
     };
 
-    typedef void (*ChangeCallback)(ButtonState);
+    using ChangeCallback = std::function<void(ButtonState)>;
 
     Common::Schedule::NextTime execute() override;