[Feature] Embed consensus types in rpc types wherever possible

[prestwich]

          the way to enforce it as a bound on network (if we even want to do that) would be to have `type TransactionResponse: RpcObject + AsRef<Self::TxEnvelope>`, basically. That would ensure that any response object contained an envelope

I think that the longer we go without embedding consensus objects in the RPC types, the worse of a time we'll have making the change

My primary target list is

• Log
• TxEnvelope (deferred for now)
• ReceiptEnvelope

Originally posted by @prestwich in #361 (comment)