Update KDE logo to be closer to original

Summary:
Make the colors and rounded square closer to the newest original logo.

Middle: Original
Left/Right: Breeze

Test Plan: Open Cuttlefish and search for "kdeapp".

Reviewers: VDG, KDE Promo, filipf

Reviewed By: filipf

Subscribers: abetts, ndavis, filipf, ngraham, KDE Promo, kde-frameworks-devel, VDG

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D20342