refactor layout.h into single file per Node* classes

engine/node_button.h

@@ -0,0 +1,24 @@
+#pragma once
+#include "node.h"
+#include "node_border.h"
+#include "node_text.h"
+
+class NodeButton : public Node
+{
+public:
+    NodeBorder* m_border;
+    NodeText* m_text;
+    glm::vec4 color_normal{ .1, .1, .1, 1 };
+    glm::vec4 color_hover{ .2, .2, .2, 1 };
+    glm::vec4 color_down{ .3, .3, .3, 1 };
+    std::function<void(Node* target)> on_click;
+    virtual Node* clone_instantiate() const override;
+    virtual void clone_children(Node* dest) const override;
+    virtual void clone_copy(Node* dest) const override;
+    virtual void init() override;
+    virtual void create() override;
+    virtual void loaded() override;
+    virtual void parse_attributes(kAttribute ka, const tinyxml2::XMLAttribute* attr) override;
+    void set_color(const glm::vec4& c);
+    virtual kEventResult handle_event(Event* e) override;
+};