save fluxes of certain targets in realtime

[lspitler]

To further reduce write-to-disk size, we can save photometric fluxes for specific targets. Ideally this should not reduce frame rates, so threading might be useful. Or a queue system.

Requires #5 to be implemented potentially, or simply do this across whole image. Similar input format as #5 .

It would require flat fielding first. Or maybe that can be done in post-processing if the thumbnails are also saved. But let's not assume thumbnails are stored for this and require the user to point to a suitable flat field image: flat_field_image

Steps for each target would be:

1. centroid on expected position
2. measure and record fwhm (need later for aperture correction)
3. aperture photometry given aperture_size and sky_radius sky_annnulus_width

Fine to store as raw fluxes.