Transform M2FS to i-band

[kadrlica]

The magnitudes in the M2FS table is currently g-band magnitude. This is because the M2FS velocities are coming from Mg lines, which are at ~5170 Angstroms or ~g-band. So for M2FS we should be using g-band magnitudes for the S/N calculation. However, right now when we simulate the isochrones of dwarfs we are using the i-band stellar magnitude to calculate the S/N for all instruments. So either we need to transform the M2FS.dat table to i-band (probably easiest structurally) or we need to pass in g-band magnitudes for the M2FS instrument (a bit more difficult, but do-able).