Hard-code software acknowledgements

[joeroe]

We are required to acknowledge the use of a variety of resources (e.g. icons, services), which we currently do at https://xronos.ch/about/acknowledgements. However, this is just saved in the database, meaning that anyone running XRONOS with their own data would be missing them.

It would be more suitable for software-related acknowledgements to be hard-coded into the software itself, e.g. in the footer, as a special page and/or in the README.