Graphics: Replace RenderFrame by RenderResources

This changes makes the whole rendering independent from the RenderFrame acquired from the Swapchain.
This may allow to do offscreen rendering (= without swapchain), or multi-window rendering in the future

include/Nazara/VulkanRenderer/VulkanRenderImage.hpp

@@ -31,7 +31,7 @@ namespace Nz
 
 			inline Vk::Fence& GetInFlightFence();
 			inline Vk::Semaphore& GetImageAvailableSemaphore();
-			inline UInt32 GetImageIndex();
+			UInt32 GetImageIndex() const override;
 			inline Vk::Semaphore& GetRenderFinishedSemaphore();
 			VulkanUploadPool& GetUploadPool() override;