This PR mainly refactors the code by extracting a "core" package which
is then used by the "backend" and "frontend" apps.
Apart from this the PR also contains several smaller changes like fixing
dependabot, upgrading dependencies, aligned "package.json" files, added
tests, ...
addresses step 1 of #32closes#136
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Co-authored-by: Marco Pasqualetti <marco.pasqualetti@live.com>
- add a few tests
- re-organize tests to allow testing with different env vars and
creating a combined coverage report
- extract test data into separate files, because importing data from
testA in testB leads to weird jest errors
- remove `dotenv` because it's not being used
- "GitHub Trends" -> "GitHub Stats Extended"