16 bit saving now works!

Did a somewhat major refactor of the image and yaml saving code. There
are now mostly separate functions that are hopefully more
comprehensible.
have epix use upper bits of a 16 bit image so that output tiffs look right when viewed in normal image viewers
convert DummyCamera to also use upper 16 bits (or actually just always give a 16 bit large image. A little reoganization in camera_controller