De-interlace reference pixels ASAP

The Interleaved Reference Pixels come off the ASIC, well, interleaved. There is no case where we care about the interleaving later on, and many where we want them separated into a data image and a reference pixel image. No information is lost by de-interlacing.

So split them out as early as possible: treat the DAQ as returning two images. Do not expand any N-1 reference pixels – that is for a different layer.