Clone candidate before altering its PID property
Currently, if a particle is accepted for mapping onto a new particle ID (PID), the original copy of the candidate (which might be owned by a module upstream of the IdentificationMap instance) is altered. This may have unintended consequences. For example, what if the intent is not to alter the original particle, but rather to create a new list of particles with alternate PID settings? If one alters the original candidate's PID setting, then after-the-fact it's not possible to compare how the PID algorithm performed (e.g. you lose the ability to do efficiency and mis-identification studies to cross-check the implementation of the IdentificaionMap in the first place).
This change clones the candidate before then altering its PID variable and storing it in the output list.
