Pid Stage

Hi Sebastian,

Here is the final stage of the pisa template generation step. A bit of an explanation is required here:

1. This is currently done exactly as it is in PaPA, because I don't think we've discussed exactly how to do PID directly from simulations.
2. My thought on doing PID directly from simulations would be similar to the 2D kernels of reconstruction, where for each (```energy, coszen```) bin of each type (```nue_cc, numu_cc, nutau_cc```) we have a kernel which computes what the distribution of events are id'd as tracks or cascades. What do you think?

I've tested this version and I think it works correctly, but I need to do a few more checks on it to be sure.