Utility/Window: Add new event system, based on signals

Old pooling-based system remains for now but is now deprecated


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Former-commit-id: 71893d639b5e1628776d8a4577b0309437865c16

SDK/src/NDK/Application.cpp

@@ -26,6 +26,8 @@ namespace Ndk
 		{
 			Nz::Window& window = **it;
 
+			window.ProcessEvents();
+
 			if (!window.IsOpen(true))
 			{
 				it = m_windows.erase(it);