choice of maxgamma

maxgamma will be set to 4 as default, so all ME predictions will have 4 GeV as lower bound.
Currently ttbar still has 1 GeV as ttZ went down to 1 GeV mll. At the same time tWZ had a lower cut of 30 GeV, so the default of 10 is used for maxgamma. 
ST_wtch_DR and hvq in Powheg/SingleT as well as Powheg/TT needs to be updated. 