Cleanup PixelModuleData, part 1

First part of cleanup of PixelModuleData with the aim of:

• do not silently return default values, throw an exception instead
• avoid casting as much as possible
• return by reference if possible

The motivation is to start preparing the infrastructure for ITk and at the moment we can share the majority of it with InDet Pixel. In the future we may want to reorganise this a bit as some (default) values could probably be moved to clients directly (e.g. charge calibration defaults).

This MR is not supposed to change the output but it may break Run 1. Still testing so keeping draft while allowing people to already provide feedback.

/cc @stsuno @battagl @sroe @nstyles @npetters