consider turning ewma circ priority back on

When we switched to consensus method 12, we lost the threshold of votes required to set CircuitPriorityHalflifeMsec in the consensus. So EWMA has been off.

Is this actually bad? Recent preliminary results from Shadow and ExperimenTor show that the ewma circ priority feature is actually not helpful.

In any case, we should make an explicit decision rather than just getting dumped into the current situation.