Check for distorted PSFs within the PSF library file

[bhilbert4]

At the moment, Mirage uses the to_griddedpsf() function from webbpsf to read in the gridded PSF library. However, Mirage is only reading the 0th extension of the file. However, if the PSFs include distortion, then they will be saved in the 1st extension of the fits file, based on the webbpsf documentation.

We should update our calls to to_griddedpsf() such that it reads in extension 1 if it exists and if not, fall back to extension 0.
There are 2 calls to to_griddedpsf() in psf_selection.py. Make sure to apply this to both.
https://github.com/spacetelescope/mirage/blob/master/mirage/psf/psf_selection.py#L397