Extend the bias shift correction algorithm of CALACS to handle the WFC 512 and 1K subarrays

[mdlpstsci]

This is a place-holder issue to extend the bias shift correction in the BLEVCORR step of the ACSCCD algorithm of CALACS to handle the WFC 512 and 1K subarrays. Currently, the algorithm depends upon the data having both physical and virtual overscan. The virtual overscan is not present in the 512 and 1K subarray data so the team needs to define an alternative value to be used for the algorithm.