Improve fetching a single a NFT #31
Description
Low priority as the current method works.
As of #20 this is done by passing the tx output reference received from listing all NFTs, and will fail if the NFT has been bought. Ideally this should be done by passing a unique identifier for the NFT (see mlabs-haskell/nft-marketplace#212), and have the contract do the work of tracking down the most up to date information for that NFT. Having a chain index and some kind of cache of NFT information would probably help this.