Use a Kolf icon with nice background and shadows

Summary:
Improve the Kolf icon with a golf ball with hills and the sky in the background as well as the Breeze-typical shadows.
As suggested in T10243: Some KDE applications could use better icons.

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Reviewers: VDG, KDE Games, ndavis

Reviewed By: VDG, ndavis

Subscribers: GB_2, ndavis, yurchor, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D17969