Contact diary date formatting (DEV) (#2109)

* extracted patterns

* - unexpected empty line

* fixed encoding issues

* was too complicated before

* trying to live with different implementations

* make everybody happy

* pattern test

* more normalizing

* improved readability

* team wants to hardcode everything

* ktlint

Co-authored-by: Ralf Gehrer <ralfgehrer@users.noreply.github.com>