D25265: Support adding a contact to a specific backend

[Jonah Brüchert]

jbbgameich added a reviewer: Plasma: Mobile.

REPOSITORY
  R307 KPeople

REVISION DETAIL
  https://phabricator.kde.org/D25265

To: jbbgameich, apol, #plasma:_mobile
Cc: kde-frameworks-devel, LeGast00n, GB_2, michaelh, ngraham, bruns