Better separate protocol state vs current protocol version

[jakrawcz-rdx]

Summary

When working on "staged instantiation" (needed for https://radixdlt.atlassian.net/browse/NODE-648) I noticed a refactoring opportunity: the "current protocol version" wasn't really updated by TransactionTracker, and it was a bit confusing that it is a part of ProtocolState. Now it is a separate piece of ProtocolManager's state, clearly updated only as the last step of a protocol update execution process.

Details

Please see one TODO that I added after noticing a theoretical deficiency of the today's TransactionSeriesExecutor. I really believe we should address it soon, if we don't want to be surprised.

Testing

No behavior changes, only regression tests need to pass.