ACL sync support

[jbornemann]

Currently we ignore rep:ACL nodes, as these nodes can not be written directly. We should add support for these nodes, especially for making #65 feature more useful.

Some reference code:

import org.apache.sling.jcr.base.util.AccessControlUtil

final principleManager = AccessControlUtil.getPrincipalManager(session)
final principal = principleManager.getPrincipal('test') 
println principal.getName()
final perms = ['jcr:all'] as String[]
AccessControlUtil.replaceAccessControlEntry(session, '/content/test', principal, perms, null, null, null)
session.save()