CDELT1/CDELT2 updates for WFC3 and ACS

[stscicrawford]

SCSB is to supply the appropriate WCS keywords that should be added to NPOLFILE that are accurate and sufficient that the files are compliant with the FITS standards such that they pass fitsverify without any warning.

cc @stsci-hack @nden @mdlpstsci

[mdlpstsci]

The implicit statement here is that SCSB will work with the instrument teams to determine the appropriate WCS keyword values in a "do no harm" manner to mitigate any inappropriate interpretation of the data in the reference files. Since AstroDrizzle uses the CDELT1/CDELT2, it would be useful to understand what default values the software uses for the remaining WCS keywords - under the assumption the software actually needs the values from the remaining WCS keywords for its computations.