Adding versioning in ZDC calibration files via parameter for TDirectory name
The current ZDC calibration files on EOS have a single version in the top directory, but we need some means to add versioning in the near future. The simplest scheme I have is moving all calibration objects to individual Directories ("v1/", "v2/", etc.) and this is what is implemented here. If no version is specified, it defaults to the top TFile directory.