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

feat: SelectArticleList control; refactor: ArticleList / Article -> more options to control behaviour and better inheritance