Discussion on Standard for onchain storing NFT's metadata

[thomasnft]

This issue is opened for discussion on a new Standard for onchain storing NFT's metadata, enable smart contracts to write or read data of specific NFT for business logic needs.
Key points:

1. Each Dapp owns a Data-registry for storing NFT's metadata in terms of key - value.
2. The standard complies with all KIP-17 (ERC-721) tokens.
3. Only Dapp or authorized agent is eligible for writing (updating) NFT's metadata.

This issue number will be used as a KIP number.