Include IPFS gateway address for NFT avatars using IPFS CID

[livid]

For example, for vitalik.eth:

https://api.planetable.xyz/ens/resolve/vitalik.eth

The avatar field should return:

https://gateway.ipfs.io/ipfs/QmSP4nq9fnN9dAiCj42ug9Wa79rqmQerZXZch82VqpiH7U/image.gif

Instead of the current response:

ipfs://ipfs/QmSP4nq9fnN9dAiCj42ug9Wa79rqmQerZXZch82VqpiH7U/image.gif