Don't apply configs in a loop

Summary:
Loop through all the changed bits then apply at once. It should trigger
less unnecessary visual changes.

Test Plan:
Restarted kded5, restarted the computer too at some point.
Connected and disconnected displays.

Reviewers: broulik

Reviewed By: broulik

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D15767