color monochrome icons to tooltip colors

Summary:
when the tooltips are dark, monochrome icons can be black on black
use kiconloader with a custom palette to color any eventual monochrome icon

Test Plan: monochrome icons appear white

Reviewers: #plasma, sitter

Reviewed By: sitter

Subscribers: broulik, ngraham, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D19596