This patch recreates the exiting panel button graphics in
the qtcreatoricons.svg file. We can now create @2x versions.

The border-image borders are corrected to 3 pixels. The panel
manage button has now centered arrows.

The addidtion of the @2x versions will be done in another commit.

Change-Id: I287e1c902f187deefc65524fdd6056067ab017de
Reviewed-by: Alessandro Portale <alessandro.portale@digia.com>