Merge branch 'master' of http://github.com/radio-astro-tools/spectral-cube

# By Adam Ginsburg (keflavich) (167) and others
# Via Adam Ginsburg (44) and others
* 'master' of http://github.com/radio-astro-tools/spectral-cube: (231 commits)
  update apt-get listings (fixes graphviz install issue)
  bugfix: with_mask should be usable when no `_mask` is defined
  clean up tests of broadcastability
  with_mask checks for broadcastable, not equal shape
  add 'save' to quicklooks
  updated CHANGES
  fix a merge mistake in spectral quicklook
  need to pass CASA's units into SpectralCube (also, should check for importerror with aplpy quicklooks)
  fix CASA .image reading: should not assume 3d by default, since usually stored as 4d
  add a quicklook tool for spectral slices
  fix spectral quicklook wcs
  add quick_look documentation
  add a quicklook tool for spectra
  docstring for to_pvextractor
  add a simple to_pvextractor tool
  fix FITS reading bug
  Add Zenodo DOI
  add start_gui keyword
  autoload glue viewer
  need to check component labels, not 'components'
  ...

Conflicts:
	.travis.yml
	CHANGES.rst
	spectral_cube/masks.py
	spectral_cube/spectral_cube.py
	spectral_cube/tests/test_masks.py