Exclusion of user specified phi-range from RM synthesis band-averaged images

[sposullivan]

I would like to have the option to exclude a specified range in Faraday depth during peak finding in the RM cube for the creation of the band-averaged maps. This is useful for observations where the wavelength-squared coverage is large enough (or the target RM high enough) such that the instrumental polarization peak is separated from the real polarized emission by more than one FWHM of the RMSF.