Uncomment checksum assert in IRF tests
Adds to gammapy.datasets scripts to load fermi extended source catalog images
Adds fermi extended sources test case
Merge pull request #152 from ellisowen/extended_sources

Extended sources
Adds FermiVelaRegion load scripts to datasets
Adds unit test for Fermi Vela Region
Adds supporting changes in setup_package.py for new FermiVelaRegion class
Merge pull request #156 from ellisowen/fermi_source_data

Fermi source data
Changed and fixed cov2corr
Merge pull request #159 from adonath/cov_to_corr

Changed and fixed cov2corr
Implemented distributions as astropy models

Conflicts:
	gammapy/astro/population/spatial.py
Changed all models to astropy models added testing and docs
Changed code to use quantities