Fix dialing via KDE Connect, and make it the default

Summary:
Let's rather promote our own stuff rather than proprietary alternatives.
Same should be done for the SMS case, but so far I failed to make that
work properly (ie. with content) with KDE Connect.

Reviewers: dvratil

Reviewed By: dvratil

Subscribers: mlaurent, dvratil, kde-pim

Tags: #kde_pim

Differential Revision: https://phabricator.kde.org/D20353