Moved menu code into GUI

Button events are now sent when you click.

src/Engine/GUI/MainMenuSystem.cpp

@@ -0,0 +1,37 @@
+#include "GUI/MainMenuSystem.h"
+
+MainMenuSystem::MainMenuSystem(SystemParams params, IRenderer* renderer)
+    : System(params)
+    , ImpureSystem()
+    , m_Renderer(renderer)
+{
+    EVENT_SUBSCRIBE_MEMBER(m_EPressed, &MainMenuSystem::OnButtonPress);
+    EVENT_SUBSCRIBE_MEMBER(m_EReleased, &MainMenuSystem::OnButtonRelease);
+    EVENT_SUBSCRIBE_MEMBER(m_EClicked, &MainMenuSystem::OnButtonClick);
+}
+
+void MainMenuSystem::Update(double dt)
+{
+
+}
+
+bool MainMenuSystem::OnButtonClick(const Events::ButtonClicked& e)
+{
+    printf("\nClicked: %s", e.EntityName);
+    return true;
+}
+
+bool MainMenuSystem::OnButtonRelease(const Events::ButtonReleased& e)
+{
+    printf("\nReleased");
+
+    return true;
+}
+
+bool MainMenuSystem::OnButtonPress(const Events::ButtonPressed& e)
+{
+    printf("\nPressed: %s", e.EntityName);
+
+    return true;
+}
+