Initial restructuring of noise items in config.  Add a new noise.py file for them.
(#364)
Restructure the noise functions to use valid_noise_types dict and single AddNoise function for each type.  Simplifies code substantially and leads to more code reuse.
(#364)
Add image.copyFrom function to python Image class
(#364)
Add makeSkyImage function
(#364)
Remove sky_level_pix option in config.
(#364)
Use makeSkyImage in config and in demo9 to do the right thing for variable sized pixels
(#364)