BUG 1758 - Clustering : CompositeModificationPayload ClassNotFoundException

This patch also fixes BUG 1753 by enabling the SLF4J Adapter so that logging
goes to the karaf log.

For the most part the fix for CompositeModificationPayload not being found
is because of a DynamicImport missing in sal-akka-raft. I've also moved
Payload and CompositeModificationPayload to sal-clustering-commons

Change-Id: I82f6f598b8c912f8109526ebe7340c70f52fdcde
Signed-off-by: Moiz Raja <moraja@cisco.com>
Merge "BUG 1758 - Clustering : CompositeModificationPayload ClassNotFoundException"