Make new Noise heirarchy, so far with just CCDNoise as a derived class
(#349)
Add DeviateNoise to enable adding noise according to a given BaseDeviate
(#349)
Add sky level to CCDNoise
(#349)
Add GaussianNoise and PoissonNoise
(#349)
Make addNoiseSNR use new Noise classes
(#349)
Incorporate new Noise classes into demo scripts
(#349)