Update loops to use ranged based C++11

We prefer `for (auto& i_elec : *zf_electrons) {` to
`for (
    std::vector<ZFinderElectron*>::iterator i_elec = zf_electrons->begin();
    i_elec != zf_electrons->end();
    ++i_elec
) {`

Also clean up a few left over spaces at the end of lines.