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/OpenGLRenderer/OpenGLRenderImage.hpp

@@ -24,15 +24,19 @@ namespace Nz
 
 			void Execute(const FunctionRef<void(CommandBufferBuilder& builder)>& callback, QueueTypeFlags queueTypeFlags) override;
 
+			UInt32 GetImageIndex() const override;
 			OpenGLUploadPool& GetUploadPool() override;
 
 			void Present() override;
 
+			inline void Reset(UInt32 imageIndex);
+
 			void SubmitCommandBuffer(CommandBuffer* commandBuffer, QueueTypeFlags queueTypeFlags) override;
 
 		private:
 			OpenGLSwapchain& m_owner;
 			OpenGLUploadPool m_uploadPool;
+			UInt32 m_imageIndex;
 	};
 }