- implemented afterAdminUnlinkedCellphoneContactDataEvent() which observes events being fired after cellphone has been unlinked from contact
- also checked if contact and cellphone are really linked
- renamed message key to ERROR_BEAN_HELPER_CELLPHONE_NUMBER_NOT_SET as this reflects what is there
- added missing i18n message
Signed-off-by: Roland Häder <roland@mxchange.org>