Contract: Check for ContractMetadata

When only NFT contract address is given, first thig to check - call nft_metadata method on the contract.

if error: display error message saying given contract is not compliant with NEAR NFT standard
if success, response must be some JSON.

Full JSON:

{
  spec: string, // required, essentially a version like "nft-1.0.0"
  name: string, // required, ex. "Mochi Rising — Digital Edition" or "Metaverse 3"
  symbol: string, // required, ex. "MOCHI"
  icon: string|null, // Data URL
  base_uri: string|null, // Centralized gateway known to have reliable access to decentralized storage assets referenced by `reference` or `media` URLs
  reference: string|null, // URL to a JSON file with more info
  reference_hash: string|null, // Base64-encoded sha256 hash of JSON from reference field. Required if `reference` is included.
}

spec, name and symbol are required:

warning if any is empty.
display as is if present

epam / near-nftchecker

Contract: Check for ContractMetadata #2