- pass short_description to header.html include statement in templates/setup.html
- pass description to header.html include statement in
modules/sharing/templates/sharing.html
- use `[]` instead of `None` for the initial value of description
property in SetupView (plinth/views.py)
- add license info to header.html
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>