apply extinction

[pbrown801]

For best comparison, within mangle_data the template spectrum should be reddened by the host reddening, then redshifted to the observer frame, then reddened by the MW reddening, then mangled.

One output csv should be the spectra in the observer frame with the spectra mangled to the observed photometry.

Those output spectra should then be dereddened by the MW reddening, deredshifted, dereddened by the host reddening, and converted to luminosity using the distance.

The extinctions should be given as input or read in from the swift supernova csv file.

https://extinction.readthedocs.io/en/latest/