GH actions (docker&python lint, greetings, stale)

[espenhgn]

Fixes #44

Changes proposed in this pull request:

• Adds some basic GitHub actions from https://github.com/precimed/container_template.git
• Added python test loading explicitly installed packages

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• I've read and followed all steps in the Making a pull request
  section of the CONTRIBUTING docs.
• If this PR adds a new feature, I've added tests that sufficiently cover my new functionality.

[ofrei]

Looks good!
What about piping yes into the pip install commands? According to https://superuser.com/questions/816143/how-to-run-pip-in-non-interactive-mode that's the way to go for non-interactive pip installations.

Or is this only relevant if pip install pulls dependencies, and we'd rather like to list those dependencies manually, with benefit being that we'll have more control over versioning?

[espenhgn]

Looks good! What about piping yes into the pip install commands? According to https://superuser.com/questions/816143/how-to-run-pip-in-non-interactive-mode that's the way to go for non-interactive pip installations.

Or is this only relevant if pip install pulls dependencies, and we'd rather like to list those dependencies manually, with benefit being that we'll have more control over versioning?

I believe piping "yes" is redundant these days. The question on that page is eight years old :)
I changed it in this PR as the docker file linter that I added complained about it. Dependencies should be installed automatically.