SLING-3030 : add a 'convert to sling content-package project' action to the context-menu for a Project under 'Configure' : sets the 'sling-content' facet and configures the jcr_root

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1518664 13f79535-47bb-0310-9956-ffa450edef68