Creation of model images and image measurements
Merge pull request #65 from adonath/model_image_creation

Creation of model images and image measurements
Minor fixes to morphology/model.py
Add gammapy/morphology/tests/test_model.py
Added plotting.py and blue_red_colormap
Added containment radius/fraction methods.
Added gaussian_sum_moments
Added formulae to docs
Merge pull request #66 from adonath/red_blue_colormap

Added plotting.py and blue_red_colormap
Merge pull request #67 from adonath/add_image_measure_methods

Add image measure methods
Extend image plotting colormap functions.
Minor cleanup of image measure and Gauss morphology functions