While a Space is undergoing Evolution, it should be locked

Summary: Currently, there is a rare but terribly dangerous race condition in querki.evolutions.Evolutions. This is a process that runs a relatively long time, and I have no confidence that, if it starts on two machines simultaneously, it won't product horrible brokenness.

This is probably a special case of the notion that, as soon as one node begins opening a Space, it owns it immediately.