Changes to Travis CI pricing

[StefanBrand]

It should be checked, what the impact of this new situation is: https://blog.travis-ci.com/2020-11-02-travis-ci-new-billing

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Overview: https://docs.github.com/en/free-pro-team@latest/actions/learn-github-actions/migrating-from-travis-ci-to-github-actions

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We need to:

• [ ] run Python scripts to download and parse angels and events, e.g. https://docs.github.com/en/free-pro-team@latest/actions/learn-github-actions/migrating-from-travis-ci-to-github-actions#migrating-phases-to-steps
• [ ] deploy to gh-pages branch
• [ ] repeat regularly (Travis limited us to daily runs. GitHub actions allows for runs up to every 5 minutes), e.g. https://futurestud.io/tutorials/github-actions-trigger-builds-on-schedule-cron

Possibly useful actions:

• https://github.com/marketplace/actions/github-pages-action
• https://github.com/marketplace/actions/deploy-to-github-pages