feat: UserData -> auto-insert contact person email address when selecting contact person via address

fix: UserData -> set all unset attributes to false instead of undefined; always trigger change on customer select; fix: address select load correct address

refactor: UserData -> show placeholders for contact person / mail; do not auto-fill contact person / mail

fix: workaround for composer bug - Uncaught TypeError: rtrim() expects parameter 1 to be string, bool given

fix: quiqqer/order#145

Closes order#145

See merge request !3

refactor: remove debug logs

See merge request !2

fix: invoice#127

Closes invoice#127

See merge request !1