Move officeimporter plugin functionality to wysiwyg top-level menu

Currently officeimporter functionality is integrated into wysiwyg editor as a tool-bar feature. This needs to be moved into wysiwyg top-level menu. Refer http://www.mail-archive.com/devs@xwiki.org/msg11286.html and http://www.mail-archive.com/devs@xwiki.org/msg11317.html for details.