nftMarker struct with addNftMarker returning it

[kalwalt]

This PR add the feature Position: in the addNFTMarker method retrieve the id, dpi, width, height of the marker, so are available for calculate the 3D obj onto the NFT marker with this calculation:

obj.position.y = (msg.height / msg.dpi * 2.54 * 10)/2.0;
obj.position.x = (msg.width / msg.dpi * 2.54 * 10)/2.0;

linked PR kalwalt/jsartoolkit5#42