Improve NIR linearity corrections

The h4 linearity corrections need work, with two significant algorithmic changes:

• corrections must be applied before UTR fitting and not to the 2-d image
• changes in UTR rates across a ramp can be used to reject badly-linearized pixels.

and a couple of processing/book-keeping changes:

• masking of pixels with poor/invalid fits was sometimes sloppy.
• cosmic rays and ASIC glitches should be detected and masked.

One big part of this work is done in a separate ticket: splitting the ramps to detect badly linearized pixels. [ Also better treatment of ASIC glitches, but that is lower priority ]