Add Marcus polaron recombination mechanism

[MikeHeiber]

Currently, only Miller-Abrahams model is implement for polaron recombination, and it would be nice to add option to enable a Marcus model instead, which would allow one to test the inverted regime for large donor-acceptor energetic offset. However, in practice, large donor-acceptor energy offset is not common (at least for PV) because it produces a low Voc. The Marcus is recombination event class is already created in the Polaron class, but it needs to be used in the OSC_Sim::calculatePolaronEvents method.