ENH: Associated icon with copy, cut and paste action

Icons are licensed under Creative Commons License (CC-BY-SA 3.0)
See http://creativecommons.org/licenses/by-sa/3.0/

They have respectivaly been downloaded from:
 http://openiconlibrary.sourceforge.net/gallery2/?./Icons/actions/edit-copy-6.png
 http://openiconlibrary.sourceforge.net/gallery2/?./Icons/actions/edit-cut-6.png
 http://openiconlibrary.sourceforge.net/gallery2/?./Icons/actions/edit-paste-6.png

Before being uploaded on "openiconlibrary", the icons originally have
been obtained from http://www.oxygen-icons.org/

git-svn-id: http://svn.slicer.org/Slicer4/trunk@21618 3bd1e089-480b-0410-8dfb-8563597acbee