New virtualbox icon

Summary:
BUG: 384357

Here's a candidate for a virtualbox icon.

Should be completely in line with breeze specs.

Reviewers: Breeze, ngraham, VDG, andreaska

Reviewed By: Breeze, ngraham, VDG, andreaska

Subscribers: ltoscano, davidc, Frameworks

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D10212