Integrate render target handling in frame graphs (#411)

* Graphics: Integrate RenderTarget in FrameGraph

- This handles the blit to texture/swapchain in the FrameGraph and fixes RenderTextureBlit
- Dummy attachments were added to the FrameGraph class to handle link without texture (used to setup a dependency between two passes with no texture)
- FramePass now supports custom access/layout/usage for inputs

* Graphics/RenderTarget: Allow to set any RenderTarget as output

include/Nazara/Graphics/RenderTarget.inl

@@ -6,6 +6,32 @@
 
 namespace Nz
 {
+	inline RenderTarget::RenderTarget(Int32 renderOrder) :
+	m_renderOrder(renderOrder),
+	m_frameGraphOutput(false)
+	{
+	}
+
+	inline Int32 RenderTarget::GetRenderOrder() const
+	{
+		return m_renderOrder;
+	}
+
+	inline bool RenderTarget::IsFrameGraphOutput() const
+	{
+		return m_frameGraphOutput;
+	}
+
+	inline void RenderTarget::SetFrameGraphOutput(bool output)
+	{
+		m_frameGraphOutput = output;
+	}
+
+	inline void RenderTarget::UpdateRenderOrder(Int32 renderOrder)
+	{
+		OnRenderTargetRenderOrderChange(this, renderOrder);
+		m_renderOrder = renderOrder;
+	}
 }
 
 #include <Nazara/Graphics/DebugOff.hpp>