fontinst quits after KJob is done

Summary:
As the summary says, when installing/removing multiple fonts to system the expected behaviour would be for fontinst to keep running after the first font has been installed or removed, instead it quits which causes a bunch of issues. fontinst uses KJob to authorize and internally KJob uses a QEventLoopLocker which causes the main event loop to quit when it's done.
I'm not entirely sure why the event loop locker is enabled by default for KJob, but the patch I have attached works around this by completely disabling that functionality for fontinst. There's a timer that runs in the background which checks for any connected clients, so it will quit after a little while regardless.

BUG: 379524
BUG: 379324
BUG: 349673
BUG: 361960
BUG: 392267

Test Plan: Make sure fonts are still installed and removed properly.

Reviewers: Plasma, dfaure, aacid, gateau

Reviewed By: dfaure

Subscribers: wbauer, ngraham, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D14493

(cherry picked from commit 60c895758f20bd2cb17ab12e57cf34cc37197098)