It's now a Tick that locks down event order. Before this change, the
event order would be locked down in the order the server sees it.
Fixes#59Fixes#61
When in tick-less mode, no longer continuously hash on the
background thread. That mode is just used for testing and
genesis log generation, and those extra hashes are just noise.
Note that without the extra hashes, with lose the duration between
events. Effectively, we distinguish proof-of-order from proof-of-time.