Initialization: cutoff distance between electron sites and hole sites

[vpasumarthi]

https://github.com/vpasumarthi/KineticModel/blob/2a0a0057f36d32befc003d04c2eee6fba2426d3c/SourceCode/KineticModel.py#L807-L817

Avoid initializing electron and hole sites within a given cutoff radius.