To prevent replay across chains, eg from ropsten to mainnet.
Additionally, this introduces a version number, so we won't have to
worry about future signature formats being accidentally compatible with
this one.
Also switches everything to ropsten by default, including ivory pill.
Batches work on ropsten now.
Also adds +tx as a hacky development tool to create text for metamask to
sign and then turn that into a batch. A useful reference for bridge and
aggregator work.
