Graphics: Rework shadowing (add cascaded shadow mapping)

- Add support for per-viewer shadows
- Add cascaded shadow mapping for directional lights (wip)
- Rework the way lights are sent to the shaders (they are now selected once per viewer)
- Fixes PointLight shadow mapping (using a dedicated pass)
- Lights out of frustum for every viewers are no longer processed (wip)

include/Nazara/Graphics/SpotLightShadowData.inl

@@ -6,6 +6,10 @@
 
 namespace Nz
 {
+	inline const ViewerInstance& SpotLightShadowData::GetViewerInstance() const
+	{
+		return m_viewer.GetViewerInstance();
+	}
 }
 
 #include <Nazara/Graphics/DebugOff.hpp>