New virtualbox icon

Summary:
BUG: 384357

Here's a candidate for a virtualbox icon.

Should be completely in line with breeze specs.

{F5685815}

{F5685789}

Reviewers: #breeze, ngraham, #vdg, andreaska

Reviewed By: #breeze, ngraham, #vdg, andreaska

Subscribers: ltoscano, davidc, #frameworks

Tags: #frameworks

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