Updates to R-Hadron simulation for stable particles

This is a couple of twweaks to double protect us when running stable R-Hadron simulation. The idea is that people should be able to not set a lifetime or set a lifetime to -1 or 0 and assume that the simulation will guess they want stable particles. Explicitly setting doDecays=0 will also work. Also added a catch in the simulation to make sure that the settings read in are consistent (e.g. if someone sets a lifetime, they almost certainly want decays, and if they set a negative lifetime they almost certainly don't).

Marking as a WIP until we can get some tests in.

This doesn't touch evgen, so not marking for 21.6 or pushing into 19.

cc: @leejr , @kpachal , @hoide , @ekuwertz