Delay load on output add/remove

Summary:
In order to give the KScreen daemon time to update the config settings after
an output has been removed or added delay the load call by one second.

Test Plan: Tested on Wayland and X.

Reviewers: #plasma, ngraham

Reviewed By: ngraham

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D24021