Normalise DiffractionFocussing output by number of contributing spectra

[Russell Taylor]

Will change the bell-shaped output to a flatter one, with larger errors at the edges and in masked regions, where fewer spectra contribute.

[Russell Taylor]

It already does this! (I must admit, though, that in the examples I've looked at it only makes a barely noticeable difference at the very edges of spectra - it certainly doesn't produce an overall flattening effect).

The only thing that we may want to change is that after this normalisation it multiplies back by a constant factor that is the total number of spectra in the group (i.e. the max value of the contribution spectra). I did this mainly to keep results largely consistent with the previous (pre-masking) version.

[Stuart Campbell]

This ticket has been transferred to github issue ​1642