Add some widget layout and ability event handling.

src/ui_elements/widgets/VerticalSpacer.h

@@ -0,0 +1,23 @@
+#pragma once
+
+#include "Widget.h"
+
+class VerticalSpacer : public Widget
+{
+    std::vector<double> mScales;
+
+public:
+    VerticalSpacer();
+
+    static std::unique_ptr<VerticalSpacer> Create();
+
+    void AddWidget(WidgetUPtr widget) override;
+
+    void AddWidgetWithScale(WidgetUPtr widget, double scale);
+
+    void AddChildLayers(const PaintEvent* event) override;
+
+    void OnPaintEvent(const PaintEvent* event) override;
+};
+
+using VerticalSpacerUPtr = std::unique_ptr<VerticalSpacer>;