[PYOPENMS] changed extra methods on MSSpectrum

    get_peaks and set_peaks now return and receive different
    precisions for mz and ii, so that we get better resolution for mz.
    mz was float32 and is now float64
Merge pull request #754 from uweschmitt/feature/pyopenms_float64_for_peaks

[PYOPENMS] changed extra methods on MSSpectrum