Our block.Block was JSONized in a bit different fashion than result.Block in
its NextConsensus and Index fields. It's not good for notifications because
third-party clients would probably expect to see the same format. Also, using
completely different Block representation is probably making our client a bit
weaker as this representation is harder to use with other neo-go components.
So use the same approach we took for Transactions and wrap block.Block which is
to be serialized in proper way.
Fix `Script` JSONization along the way, 3.0 node wraps it within `witnesses`.
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.
