refactor layout.h into single file per Node* classes

engine/node_message_box.cpp

@@ -0,0 +1,21 @@
+#include "pch.h"
+#include "log.h"
+#include "node_message_box.h"
+#include "layout.h"
+
+Node* NodeMessageBox::clone_instantiate() const
+{
+    return new NodeMessageBox();
+}
+
+void NodeMessageBox::init()
+{
+    SetPosition(0, 0);
+    SetWidthP(100);
+    SetHeightP(100);
+    SetPositioning(YGPositionTypeAbsolute);
+    m_template = (*m_manager)[const_hash("message-box")]->m_children[0]->clone();
+    add_child(m_template);
+    btnOk = m_template->find<NodeButton>("btn-ok");
+    btnOk->on_click = [&](Node*) { destroy(); };
+}