WIP: Add OverlayIconEngine to Okular
This adds OverlayIconEngine from davidhurka/overlay-icon-engine-demo> to Okular. It is intended to be useful for !141 (merged).
In this patch, the usage is demonstrated in annotationactionhandler.cpp, the advantage of a complete QIconEngine becomes visible at high toolbar scales:
(before/after, Typewriter annotation tool)
Another use case could be the Quick Annotation tool icons. These were drawn for higher resolutions, but OverlayIconEngine would support additional low resolution versions.