Fix co-authored-by comments in commits where necessary

[localheinz]

• fix co-authored-by comments in commits where necessary

After the commit message (and possible extended description), there need to be two empty lines followed by the co-authors:

Co-authored-by: Andreas Möller <am@localheinz.com>
Co-authored-by: Arne Blankerts <Arne@Blankerts.de>