Misc.: Use github action to run CI on linux and macos

[t20100]

closes #3272

[t20100]

CI working with github actions for linux, macos and windows.
It seems, it needs to be on master branch to start working, so for looking at the result, see on my fork: https://github.com/t20100/silx/actions/runs/499115931

Here is the matrix of effectively tested features:

os	GUI	OpenGL	OpenCL
linux	✓	✓	✗
macos	✓	✓	✓
windows	✗	✗	✗

[kif]

Any idea why OpenCL is failing on linux ? it should work, no ?

[kif]

I just checked with pyFAI, and the OpenCL part is also skipped on GH-actions
LGTM.

[t20100]

Thanks for the merge! Let's see how it goes...

For OpenCL on linux, only ocl-icd-opencl-dev is installed so there is probably no OpenCL device installed (I took it from our .travis.yml)

[t20100]

Looking at it, https://github.com/silx-kit/silx/blob/master/ci/intel_opencl_icd.sh is no longer called.