Plot projected SNR for LSST

[djperrefort]

The color evolution of the CMFGEN models are very similar for phases near peak B-band magnitude. To understand our ability to constrain the models in color space, we should plot the predicted SNR ratio of LSST as a function of phase and redshift (i.e., A 2d plot where SNR is a third, color axis).

This plot will involve combining information from the single visit quoted depth for LSST and a supernova model (likely Salt2).