Add saner ByteString instances

ByteString instances were removed because they allowed people to try and insert arbitrary binary data that JSON can't handle.

Could we not re-add ByteString instances that leveraged something like base64 encoding (which JSON can take I believe) to work around this limitation?

```
Fuuzetsu: Best thing to do is to avoid putting bytestrings in json,
but when it's unavoidable:
https://gist.github.com/mgsloan/bfe4bf2250c1d656a2b1 [05:03]
```

Start with the linked gist and inspect aeson's current handling of ByteString and JSON encoding. Clarify the intended base64 representation and the compatibility expectations in the discussion before identifying the implementation and test locations. Done should include an agreed approach and verified ByteString JSON behavior.

Written by the indexing model from the issue text.