Improve font selection icon

Summary:
Improves the font selection icon by making the three dots black/white instead of orange.

Test Plan: Search for gtk-select-font in Cuttlefish.

Reviewers: VDG, ngraham

Reviewed By: VDG, ngraham

Subscribers: kde-frameworks-devel, VDG

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D18855