Add email address to body of a mail notification
Summary: Also simplify/unify use of localization variables in mail templates.
Test Plan: ./phpunit tests/Unit/Mail
Reviewers: #hkccp_developers, mollekopf
Reviewed By: #hkccp_developers, mollekopf
Subscribers: #hkccp_developers
Differential Revision: https://git.kolab.org/D4746