Port printing to use the KContact::Email gadget instead of a wrapper

Summary:
This does change the theme API, however it has no practical effect as all
themes in KAddressbook are using the emails property wrongly anyway and
thus don't show anything either way.

Reviewers: mlaurent

Reviewed By: mlaurent

Subscribers: kde-pim

Tags: #kde_pim

Differential Revision: https://phabricator.kde.org/D20540