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