PowhegControl: adding runningscales option for Wt DR and DS - AGENE-2131
requested to merge atlas-physics/pmg/mcexperts/powheg-experts/athena:21.6-Wt_AddRunningScales into 21.6
This MR adds the new option runningscale for the Wt DR and DS processes. I put 1 as default (which sets some dynamic scale). Setting a negative number would fix the scales to the top mass, as far as I can see in Born_phsp.f.