implement billboard shader and add new example

openVulkanoCpp/Host/GraphicsAppManager.hpp

@@ -50,6 +50,8 @@ namespace OpenVulkano
 
 		[[nodiscard]] IRenderer* GetRenderer() const override { return renderer.get(); }
 
+		[[nodiscard]] IWindow* GetWindow() const override { return window; }
+
 		[[nodiscard]] bool IsRunning() const override { return running; }
 
 		[[nodiscard]] bool IsPaused() const override { return paused; }