add splitbox ui element

src/graphics/ui/elements/SplitBox.hpp

@@ -0,0 +1,18 @@
+#pragma once
+
+#include "Container.hpp"
+
+namespace gui {
+    class SplitBox : public Container {
+    public:
+        SplitBox(const glm::vec2& size, float splitPos, Orientation orientation);
+        
+        virtual void mouseMove(GUI*, int x, int y) override;
+        virtual void refresh() override;
+        virtual void fullRefresh() override;
+    private:
+        float splitPos;
+        int splitRadius = 2;
+        Orientation orientation;
+    };
+}