Use astropy.coords in nrao package
remove unused import
remove unused imports
Remove unused packages from sphinx mock module list
add to .gitignore
Remove old coords lib from .travis.yml
Fix astropy.units import in test_irsa_dust.py

Before there was an `import *` and I got confused.
Merge pull request #67 from cdeil/nrao_coords

Use astropy.coords in nrao module