Color icons in titlebar if possible

Summary:
Some icons can be recolored. However if the titlebar color is different
compared to the normal color scheme, this can lead to bad contrast.

Test Plan:
Before:{F8201155} {F8201159}
After: {F8201139}{F8201144}

Reviewers: #plasma, #vdg, ngraham

Reviewed By: #vdg, ngraham

Subscribers: kossebau, ngraham, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D28330