Add method to SingleCellCoadd that constructs the MaskedImage with psf

[esheldon]

cell_coadds/python/lsst/cell_coadds/_single_cell_coadd.py

Line 40 in 88a373a

class SingleCellCoadd(CommonComponentsProperties):

Downstream codes need a MaskedImage with PSF, correct wcs etc.

We need the same for the noise realizations and mfrac image

[esheldon]

I mean Exposure not MaskedImage