adding hole-ice switches.

Adding the parameters `SimulateHoleIce` and `SinglePhotonOptimizations`
to the `I3CLSimModule`.

The single-photon optimizations will change the memory allocation and
will switch off the randomization whether the photon is to be processed.

At the moment, these switches do not effect anything.

These changes are copied over from the abandoned commit
https://github.com/fiedl/clsim/commit/9c7f0e4ab90713e0ee41cda262b536e2ad
67723a.