Testing

[RemDelaporteMathurin]

This PR adds the basis of a testing framework and CI.

• new test directory
• new github actions workflow ci.yml with three jobs:
  • test frontend server
  • test backend sever + pytest
  • test both at the same time (needs the first two to pass)

[jhdark]

A good start to at least get the framework in place. I guess once the repository is public we can add the code coverage check too.