Please do not merge this yet. Various checks to be done, namely, review generator and simulation physics output.
Add new HiddenValley decay files, for various HV pion final states:
dkfiles/HiddenValley_HiggsPortal_KK_1.02GeV_5ps.dec
dkfiles/HiddenValley_HiggsPortal_KK_1.08GeV_5ps.dec
dkfiles/HiddenValley_HiggsPortal_KK_1.3GeV_5ps.dec
dkfiles/HiddenValley_HiggsPortal_KK_1.8GeV_5ps.dec
dkfiles/HiddenValley_HiggsPortal_KK_2.5GeV_5ps.dec
dkfiles/HiddenValley_HiggsPortal_mumu_0.3GeV_5ps.dec
dkfiles/HiddenValley_HiggsPortal_mumu_0.9GeV_5ps.dec
dkfiles/HiddenValley_HiggsPortal_pipi_0.4GeV_5ps.dec
dkfiles/HiddenValley_HiggsPortal_pipi_0.6GeV_5ps.dec
dkfiles/HiddenValley_HiggsPortal_pipi_0.8GeV_5ps.dec
dkfiles/HiddenValley_HiggsPortal_pipi_0.95GeV_5ps.dec
dkfiles/HiddenValley_HiggsPortal_ssbar_1.8GeV_5ps.dec
dkfiles/HiddenValley_HiggsPortal_ssbar_2.5GeV_5ps.dec