Set sdintimaging and feather kwargs for single dish data

[e-koch]

For non-ALMA data, we need to be able to pass additional properties for single dish data.

For sdintimaging and feathering, we need to be able to specify the flux scaling factor and effective dish diameter per single dish file. For sdintimaging this is these 2 keywords:

sdgain             =  1
dishdia            =  12

The defaults we currently have are appropriate only for ALMA 12-m single dish data.

The dish diameter can likely default to the beam size in the SD input file, so long as its already correct in the header.