Add Sean's approx(analytic) model code to flow

Move `Widthfun.py` to FWHM processing iPython notebook, test.
Fits work and match output from `Widthfun.py`, but errors
from lmfit confidence limits are large.
Compute `m_E` values for SN 1006 data, add 1-1.7 mosaic,
fit profiles using intensity flux instead of total counts.