Mechanism to update content of static pages

Since we have no CMS, content is directly part of the code. Should be made updateable by moderators.

We propose:

• Imprint: fetch template from https://shared.acdh.oeaw.ac.at/acdh-common-assets/api/data/ and inject specific content from some config-file from sshoc-mp-frontend-repo
• everything else About, Contact, etc.: config-files (md, yaml, whatever) in sshoc-mp-frontend-repo