Replace CircleCI with Github Actions

[milesgranger]

Should be enough to make the switch, but can be made more fancy by pulling out the deploy steps, tests, image and docs building into their own workflows later if we want.

Benefits 🦄

• Super easy matrix config, can easily run tests on different OS, python version, ...
• Better concurrency... all tests for all components start right away.. unlike CircleCI limit of 4 containers
• Less YAML

Cons 🎠

• CodeCov cannot evaluate coverage on PRs b/c running on platforms other than CircleCI, AppVeyor or TravisCI requires a token which cannot be shared with forks.
  • Releated issue: Is there a way to make this work with a PR from a fork codecov/codecov-action#29

  • Note: Token not required for public repositories uploading from Travis, CircleCI or AppVeyor.

Suppose we can store this PR until it is supported?

[epa095]

Definitely nicer than the circle setup

[EinarJohnsen]

Looks cool!

[codecov]

Codecov Report

Merging #821 into master will decrease coverage by 0.24%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #821      +/-   ##
==========================================
- Coverage   92.73%   92.48%   -0.25%     
==========================================
  Files          58       58              
  Lines        2835     2835              
==========================================
- Hits         2629     2622       -7     
- Misses        206      213       +7

Impacted Files	Coverage Δ
gordo_components/machine/model/models.py	95.55% <0%> (-2.78%)	⬇️
gordo_components/builder/mlflow_utils.py	97.03% <0%> (-1.49%)	⬇️

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