FCS shape tuning to data bug fix

This MR:

• fixes a bug where phiScaleFactor would get overwritten with the etaScaleFactor in the 2D phi_s - eta_s scaling model
• fixes an issue where we would get a crash in the FCS standalone param file merging, when the class is called using its default constructor, but no model parameter file path is defined
• improves debug level verbosity
• removes arguments from constructor and implements separate method to initialise data tuning