Send notification when screencasting fails
Summary:
A notification is sent when something
goes wrong setting up screencasting.
Test Plan:
Reviewers: Plasma, VDG, ngraham, apol
Reviewed By: VDG, ngraham, apol
Subscribers: apol, ngraham, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D28517