SLING-4106 - removed handlerId from triggers api, fixed trigger impls to be stateless, use @SlingServlet for servlets, fixed remote package exporter to get all the retrieved packages, avoid npes for session in abstract pb

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1634855 13f79535-47bb-0310-9956-ffa450edef68