Add licence declarations with reuse

[janderssonse]

This PR makes the project license declare licenses according to https://reuse.software/ so that it passes the reuse lint.

Even though it is many affected files, the pr is scroll friendly and contains no logic. It should be a quick general overview before merging it.

Basically, add adds license headers in spdx-format, as per the resuse-specification. It also adds a missing reuse LICENSES file, ofl 1.1, and the .reuse/dep5 which takes care of the licening for binary files etc.

Note: the reuse badge in the README will be green when the project is public

Note: some files created with the react-app was a bit unsure, see the comment in dep5, and it will be ok for now.

Checklist

• Changes are limited to a single goal (avoid scope creep)
• I confirm that I have read any Contribution and Development guidelines (CONTRIBUTING and DEVELOPMENT) and are following their suggestions.
• I confirm that I wrote and/or have the right to submit the contents of my Pull Request, by agreeing to the Developer Certificate of Origin, (adding a 'sign-off' to my commits).