Further customizability concerning impressum and licence

[LasseMempel]

At the moment the impressum automatically links to the hbz.
I totally agree there should be proper credit given to the SkoHub Project (like the link to the blog) and the institution behind.
Nontheless the responsibility for the vocabulary-content should be expressed and linkable to the developing institution and i can imagine vocabulary cases where the hbz wouldn't be too happy to be named.
The center of the footer would be suitable to refer to and name a licence under which the vocabulary can be reused, so for instance reuse and free distribution via open access can be encouraged.
Ideally these strings/links could be customizable via the yaml file like the title.
Cheers and thx for your terrific project!