WIP: added the possibility to choose mobility parametrisation and sensor material (Silicon or Germanium)

Two main changes:

-changed the code so that the user can specify the model for carrier mobility in the [GenericPropagation] section of the data card. The goal is to add models for carrier mobility inside sensors other than Silicon (and possibly compare different models for a given material). At the moment added a new model called "quay" (explained in the charge propagation README) which provides the mobility for a Germanium sensor. It will be easy in the future to add other models.

-the user can now specify the sensor material in the detector model data card. At the moment both Silicon (default) and Germanium are implemented. Note that the choice of material only impacts the (new) carrier mobility function in GenericProagation, the G4 material part has not yet been updated. Therefore the primary interaction and hence the number of carriers are still for Silicon. This will be changed next.