function to plot mock spectra

[eclake]

Maybe this is already available, this was just a note to say that would be nice as beagle output files are difficult for many to navigate.

[scharlot]

Also, it might be worth correcting the manual, which says that "1 file per object" is printed when selecting PRINT MOCK SPECTRUM = T

[jacopo-chevallard]

@eclake something like this exists here https://github.com/jacopo-chevallard/home/blob/master/bin/plot_Beagle_SED.py