Summary

There are some differences between NFT and ERC721, now let them converge. Here are some rough ideas:

• Add Approve function, NFT can be transferred from the owner or the approved address.
• Denom adds update_restricted field, the owner can edit the NFT only when the update_restricted is true.
• Denom adds Symbol field which is equivalent to ERC721Metadata.symbol().
• Only the Denom creator can mint NFT, or it can be optional. Add mint_restricted for it.