Make 16px folder-activites look more like larger sizes

Summary: start-here-kde/kde-plasma is symlinked to this.

Test Plan:
Old (2nd from left):

New:

Reviewers: VDG, ngraham

Reviewed By: VDG, ngraham

Subscribers: kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D23104