Add gem-sim validation modules.

Hello, experts.

These modules make plots about GEM-sim and GEM-digi validation to form DQM-like.

These are only work when VALIDATION or HARVESTING is used with gemCustum.py by cmsDriver.

Detail usage was written on https://twiki.cern.ch/twiki/bin/view/MPGD/GemSimulationsInstructionsCMSSW at VALIDATION for DIGI and HARVESTING for DIGI.