[BACKLOG-1574] - Add the ability to provide configuration to store the d...

...ata source acl nodes.

Added tag <aclNodeRoot> in ..../pentaho-solutions/system/pentaho.xml.
It is available via "public static String aclNodeRoot" in PentahoSystem or by PentahoSystem.getSystemSetting( "aclNodeRoot", "public" ). Defaults to public.

@pentaho-nbaker @diogofscmariano Please review