Support encoding Scan m/zs as doubles (instead of floats)

[PMSeitzer]

Related to #500
Should plug in to mass_spec mz binning work:
https://github.com/calico/mass_spec/issues/1224

This will require creating a function
base64::encode_base64(vector<double> mz), as a companion function to base64::encode_base64(vector<float> mz)
Note that this should plug into Scan::getBinaryEncodedData()

#500 is very extreme, it might be possible to keep scan data as doubles as an interim solution for maldesi only.