22049: ALF-3786 Partial implementation of Configurable Site Creation Group.
Site configuration groups can be configured via permissions management in the usual way.
This check-in adds hasCreateSitePermissions() to various SiteService layers to better support
client code when site creation restrictions have been imposed.
git-svn-id: https://svn.alfresco.com/repos/alfresco-enterprise/alfresco/HEAD/root@22053 c4b6b30b-aa2e-2d43-bbcb-ca4b014f7261