It's not needed any more with Go 1.13 as we have wrapping/unwrapping in base
packages. All errors.Wrap calls are replaced with fmt.Errorf, some strings are
improved along the way.
Note that the protocol differs a bit from #895 in its notifications format,
to avoid additional server-side processing we're omitting some metadata like:
* block size and confirmations
* transaction fees, confirmations, block hash and timestamp
* application execution doesn't have ScriptHash populated
Some block fields may also differ in encoding compared to `getblock` results
(like nonce field).
I think these differences are unnoticieable for most use cases, so we can
leave them as is, but it can be changed in the future.
