Add AAS astrometric residual plot code to validate_drp

As part of the work to make my poster for the AAS meeting, I put a fair bit of effort into code to make quiver plots of astrometric residuals. This code should be put somewhere more useful than my poster repository; jointcal/bin/ seems like a good choice.

The story points here include some of the effort required to write it in the first place over the break, since it's code that is directly useful to DM.