How to signal to user that features were not fit?

[drvdputt]

Currently, the rows corresponding to unused features are masked out, so that they are displayed as a row of "--" when model.features is shown in a notebook. (reminder: unused means that the feature was not fit, because is it outside of the appropriate wavelength range, as determined by the data range and the redshift). Note that this is different from a user not wanting a certain feature. In that case they should just delete it from the Features table, or comment out a line in the YAML file.

Masking was chosen as opposed to setting the parameters to nan, because the features need be able to be "reactivated", e.g. when another fit with a different redshift is passed. The mask doesn't do anything to the stored values. It is purely cosmetic.

Obvious alternative: add an "enabled" column to the Features table.

Solution by changing the design: see new issue