Add support for vote tx in nyzostrings

[AngainorDev]

Nyzo Strings currently define:

• Micropay("pay_")
• PrefilledData("pre_")
• PrivateSeed("key_")
• PublicIdentifier("id__")
• Signature("sig_")
• Transaction("tx__")

tx__ is quite useful to locally sign a transaction then send it for inclusion.
The client api has a "forward transaction" endpoint for that.

However, type 4 txs (vote) do not follow the same data structure as usual transactions and can't be encoded the same way.

Thus, we'd like to suggest a new nyzostring type - tx4_ for instance - that would represent a type 4 signed vote tx.
"Forward transaction" endpoint could then handle both tx__ and tx4_.

[n-y-z-o]

This has been corrected on https://client.nyzo.co, and the fix will be released as version 584.

The problem was actually in the run() method of TransactionForwardCommand. In building the result table, a NyzoStringPublicIdentifier was built with the receiver identifier of the transaction. This field is null for a cycle-signature transaction, and a null-pointer exception was thrown. This caused the "Unexpected issue forwarding transaction..." error.

Version 584 is already live on client.nyzo.co, so it is now able to forward cycle-signature transactions.

[n-y-z-o]

This issue has been corrected with the release of version 584. While a new Nyzo string type was not added, the current Nyzo transaction string supports all transaction types, and the issue of forwarding type-4 (cycle-signature) transactions was corrected.

[AngainorDev]

Awesome, thanks!!!