Improve emblem contrast, legibility and consistency

Summary:
Added outlines to 16 and 22 px icons
Improved the legibility of 8px icons
Added new 8, 16 and 22 px versions of existing emblems
Improved the consistency of emblem icons

BUG: 399356
BUG: 399357
BUG: 399968
FIXED-IN: 5.52

Reviewers: #vdg

Reviewed By: #vdg, ngraham

Subscribers: kde-frameworks-devel, #vdg

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D16421