Fix for interaction classification parameters which are passed to NEST.

[PavelKavrigin]

This PR fixes the issue reported here:

#43

There's one thing which needs to be clarified - what is the proper parameter to pass in case of Kr83m:

NEST.cpp#L830-L831

The mass number we pass to this function actually serves as maxTimeSeparation which is passed to

NEST.cpp#L618

We pass 'infinity' here, which makes sense. However, please look at these NEST lines to double-check it.

[HenningSE]

Good catch @PavelKavrigin, I think we could also set the mass number to 0 for all cases except Kr83m and ions. NEST has a check here looking for a mass number of 0: https://github.com/NESTCollaboration/nest/blob/cfecfdb8dc474eeff08163a361cfad58173ba93e/src/NEST.cpp#L429-L430.
In this case a random xenon isotope is used: https://github.com/NESTCollaboration/nest/blob/master/src/RandomGen.cpp#L110-L133
(I guess they are using the natural abundances of xenon isotopes here)

[PavelKavrigin]

Thanks! I've corrected it. I will run some tests now.

[HenningSE]

Thanks @PavelKavrigin, if it is running without problems we can merge the PR.