Add metadata to nft-simple

[mikedotexe]

Used what we have on the spec (transient link) https://nomicon-pr-174.onrender.com/Standards/NonFungibleToken/Metadata.html

Test with CLI via (replace mike.testnet with yours):

near create-account 171.mike.testnet --masterAccount mike.testnet && near deploy 171.mike.testnet --wasmFile res/nft_simple.wasm --initFunction new --initArgs '{"owner_id": "171.mike.testnet", "metadata": {"spec":"nft-1.0.0", "name": "Jon Gold", "symbol": "WHY"} }'

near call 171.mike.testnet nft_mint '{"token_id": "0", "metadata": {"title": "Obsidian", "description": "Black as the night"} }' --accountId 171.mike.testnet --amount 0.0079

near view 171.mike.testnet nft_total_supply ''

near view 171.mike.testnet nft_metadata ''

near view 171.mike.testnet nft_token '{"token_id": "0"}'

[mikedotexe]

I'm going to merge this in the next half hour if there are no objects, I think it's going to be harder to have a few different PRs for various NFT standards