Localizin strings and adding error checking.

apps/contacts/ajax/activation.php

apps/contacts/ajax/addcard.php

apps/contacts/ajax/addproperty.php

apps/contacts/ajax/createaddressbook.php

apps/contacts/ajax/deleteproperty.php

apps/contacts/ajax/setproperty.php

apps/contacts/ajax/updateaddressbook.php

apps/contacts/js/interface.js

apps/contacts/l10n/xgettextfiles

apps/contacts/lib/addressbook.php

apps/contacts/lib/vcard.php

apps/contacts/templates/index.php

apps/contacts/templates/part.addcardform.php

apps/contacts/templates/part.chooseaddressbook.rowfields.php

apps/contacts/templates/part.editaddressbook.php

apps/contacts/templates/settings.php