Replace logging via `iostream`s with dd4heps logging facilities

Currently there are many places where we have std::couts partially hidden behind a pre-processor DEBUGPRINT boolean variable. This could in principle be replaced with dd4hep::printout from <DD4hep/Printout.h>, which would integrate this a bit better with the DD4hep logging facilities and allow to change levels at runtime.

Originally: https://gitlab.desy.de/ilcsoft/ddfastshowerml/-/issues/1