Refs #8793 Move multi spectra plotting code to IndirectCommon.

We already have code that handles this fairly well in Bayes. We'll just
share it between the two.
Refs #8793 Remove duplicated code in IndirectBayes.

This has now been moved to IndirectCommon.
Refs #8793 Change ConvFit to plot either FWHM or Amplitude
Merge remote-tracking branch 'origin/bugfix/8793_convfit_plotting'