Add quick FITS image to bitmap conversion tool

[DaveStrickland]

It would be useful to have an internal tool that can convert a FITS image into a nicely-scaled bitmap format (e.g png, jpeg, tiff) image at 1-to-1 pixel scaling, and without external dependencies on non-python code.

The dksraw tool does this for RAW images, but not for FITS. Functions in util.ApUtil provide high quality plotting to matplotlib figures with labeling, titles, axis units and with option zooming-in, but do not generally show each and every pixel. Some of the example jupyter notebooks use Astromatic stiff tool, which does produce high quality, but this is an external tool that user's must download and install separately (+)

(+) This actually required messing around with the autoconf options when I last did this on Linux.

[DaveStrickland]

Note that astropy, which AstroPhotography depends on, has a fits2bitmap script.