RenderManager getRenderManager() {
        return renderManager;
    }
Create a standard NiftyJmeDisplay. This uses the old Nifty renderer.
It's probably slower than the batched
renderer and is mainly here for backwards compatibility.

@param assetManager jME AssetManager
@param inputManager jME InputManager
@param audioRenderer jME AudioRenderer
@param vp Viewport to use
@param colorSpace the ColorSpace to use for Nifty colors (sRGB or Linear)
jme3-niftygui/src/main/java/com/jme3/niftygui/NiftyJmeDisplay.java