Update gfz terms of use

Updated version of the terms of use.

This is the version that Almut sent on 2023-03-31. On the content I changed one single thing additionally and this was a doubled paragraph number for the GFZ liability (2 times (5)).

For the layout:

• it is based on the original layout of the old terms of use, but
• the header lines are now a level lower (h3 instead of h2).
• I use block alignment, as in the document by Almut.

Due to the changed content it resolves #215 (closed).