Set up CI with Azure Pipelines

[astrofrog]

Still needs to be done:

• Set up coverage reporting
• Determine what needs to be kept for CircleCI
• Determine what needs to be kept for Travis CI
• Determine what needs to be kept for AppVeyor
• Set up docs build
• Consider adding a configuration with old/legacy dependencies
• Build without Qt and without qt/ directories
• Decide whether to re-instate --no-optional-skip

[codecov]

Codecov Report

Merging #2060 into master will decrease coverage by 0.41%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2060      +/-   ##
==========================================
- Coverage   88.13%   87.71%   -0.42%     
==========================================
  Files         245      245              
  Lines       21493    21493              
==========================================
- Hits        18942    18853      -89     
- Misses       2551     2640      +89

Impacted Files	Coverage Δ
glue/_deps.py	56.71% <ø> (-17.17%)	⬇️
glue/viewers/profile/qt/profile_tools.py	90.08% <100%> (ø)	⬆️
glue/conftest.py	51.92% <0%> (-19.24%)	⬇️
glue/plugins/wcs_autolinking/__init__.py	85.71% <0%> (-14.29%)	⬇️
glue/_mpl_backend.py	86.36% <0%> (-13.64%)	⬇️
glue/utils/wcs.py	86.27% <0%> (-12.75%)	⬇️
glue/utils/decorators.py	58.33% <0%> (-8.34%)	⬇️
glue/utils/noconflict.py	86.04% <0%> (-6.98%)	⬇️
glue/viewers/histogram/python_export.py	90.24% <0%> (-2.44%)	⬇️
... and 15 more

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[astrofrog]

I'll punt on adding back --no-optional-skip to a separate PR, as I think it would be good to go ahead and merge this one to solve the CI issues.

[astrofrog]

The numpy/astropy dev build should be fixed once astropy/astropy#9098 is merged, and the AppVeyor failure is just due to the lack of appveyor config in the repo (this won't appear in future PRs)