Improve aperture correction

[oboberg]

I am currently working on improving the aperture correction step of the odi_phot_process.py script. The aperture correction function lives in full_calibrate.py. The current issue is that the standard deviation of the correction is still too large, even with filtering by peak counts from a fwhm measurement. I am going to see if I can implement a sigma clipping step to improve the standard deviation without throwing out too many stars.