Make it possible to stream only input
Summary: No need to share our screen contents to be able to move the mouse.
Test Plan:
Ported KDE Connect to it, works.
https://invent.kde.org/kde/kdeconnect-kde/merge_requests/199
Reviewers: Plasma, KDE Connect
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D26875