NFT with Royalty

[EGuenz]

FA2 Compliant Royalty NFT contract

Normal NFT implementation of FA2 with following changes.

1. Token metadata has following key
     royalty-data : (address %creator, nat %fee) where creator is the address that created the NFT and %fee is the percentage cut of a sale that the creator gets.
2. Owner of a token cannot transfer it— only an operator can. 
3. The contract contains no update operators entrypoint— operators must be set upon minting of some NFT and they must be set as addresses different from the token owners.
4. Operators must be KT1 addresses, which are in fact auction contracts.
5. There is an extra entrypoint Get_royalty that calculates the royalty-fee and address which is sent to the callback