Exclude conflicting artefact
Remove constructor code duplication
Specialize MessageDispatcher to FedoraMessageDispatcher
Switch to Logback backend

This enables using log levels beyond INFO.
Using JMS message handler to issue indexing jobs

Take #1
Make sure queue elements with same payload considered equal
Move IndexQueueMessageHandler out of JMS specific package
Filter JMS message subscription

- On subscribe to messages about modify, add, purge and ingest methods.
- Further separate message handlers to Datastream, Object and Relationship
  realms.
Merge branch 'messaging-refactor'