transaction with support for multiple namespaces

[akonring]

closes: #1204

Currently, the Querypayload::transaction is broken such that it only returns correct transaction if VmId indeed is 0 and there is only a single namespace:

Transaction::new(
                crate::VmId(0),
                self.raw_payload.get(tx_payload_range.clone())?.to_vec(),
            ),

This PR follows up on #1191 to have `Querypayload::transaction support multiple namespaces.

[jbearer]

In the local demo, the load generator is now receiving confirmations of the transactions it submits, which means the reported hashes must be matching the actual hashes. So I think this is working.

[ggutoski]

Hard to review on a phone but I see no problems.