add gas-specific TRT monitoring histos

Add physics validation histograms to detect variations in the number of TRT hits and hight threshold TRT hits separately for Xenon and Argon straws, as well as histograms with mu dependence that can be used for tunings. Checked histograms are filled correctly. Tagging @cgrefe, @beddall, @jchapman, @gcallea and @dhayden