Mike Perry authored Feb 21, 2017 and Nick Mathewson committed May 08, 2017

This unifies CircuitIdleTimeout and PredictedCircsRelevanceTime into a single
option, and randomizes it.

It also gives us control over the default value as well as relay-to-relay
connection lifespan through the consensus.

Conflicts:
	src/or/circuituse.c
	src/or/config.c
	src/or/main.c
	src/test/testing_common.c