advanced Process selection logic and configuration

Some processes are only applicable in very specific circumstances, e.g. muon decay only affects muons or the low energy hadronic interaction model is only applicable at low energies.
In other cases it might be necessary to limit a general process to certain cases only, e.g. in presence of the muon decay process the pythia decay routine has to be configured to not decay muons.
The current mechanism to implement this is that in case of inapplicability of a process the decay/interaction length is set to infinity, so that the process looses in the process selection for the next step.

Can/should this be done better?

Essential for: #108 (closed) #110 #1 (closed)