/transaction-info: add creator's pubkey to txindex metadata

In tandem with #297:

In `/transaction-info`, txindex metadata for both CC/DAO transfers identifies the creator by username instead of pubkey, for example:

```json
"CreatorCoinTransferTxindexMetadata": {
"CreatorUsername": "BeActive",
"CreatorCoinToTransferNanos": 10000,
"DiamondLevel": 0,
"PostHashHex": ""
}
```

This is really bad since AFAIK usernames are volatile and, even if they're not in case of already issued CCs/DAOs, it would require a second RPC call in order to grab the name's pubkey.

I would suggest improving the output of `/transaction-info` by adding the creator's pubkey in the txindex metadata.

Start at the /transaction-info endpoint and trace the txindex metadata for CreatorCoin and DAO transfers. Confirm how creator identity is currently serialized, then update the output so both metadata types include the creator's public key alongside the existing username; done means the endpoint returns that key for both transfer types.

Written by the indexing model from the issue text.