Support for loading images from an AstroPix feed.
TODO: update metadata tomfoolery to match the new things that I’ve learned. Cf.
wwtdatatool wtml report utility and the djangoplicity implementation.
NOTE: AstroPix seems to have its image parity backwards. Standard JPEGs are
wcs_scale < 0, which is positive AKA bottoms-up AKA FITS
parity. If we pass their parameters more-or-less straight through to WWT, we get
the right appearance onscreen.
An ImageSource that obtains its inputs from a query to the AstroPix service.
A CandidateInput obtained from an AstroPix query.