Create footer

This could possibly be added to the `react-digit-components`, or even fetched from there. Check with digIT members if such a header already exists.

The content of the footer could simply be the text `created with ♥ by digIT`, and possibly a link to the GitHub page or digit.chalmers.it website.

Start by checking the existing page layout and whether react-digit-components already provides a footer or related component. Confirm with digIT members which content and link are wanted, then add the agreed footer and verify that it appears consistently in the recipe bank.

Written by the indexing model from the issue text.