Save MX autoprocessing statistics cutoff in user preferences

We need to add the cutoff values in the user preference object for MX.

Currently it looks like this:

{
  //...other settings,
  cutoffs: {
    completeness: {},
    resolution_limit_low: {},
    resolution_limit_high: {},
    r_merge: { inner: 10 },
    mean_I_over_sigI: { inner: 5, outer: 5, overall: 5 },
    cc_half: {},
    cc_ano: {},
  },
}

i.e. an object for each statisic parameter with optional numbers for inner, outer and overall.

I suggest we add a cutoffs field in the existing mxsettings field of the user preference. This cutoffs field can either be typed as described above or as any to avoid having to extend it if we upload new statistics some day, up to you.