further refactoring - adding context to logs, missing comments
improvements as per peer reveiews
incorporating comments from the code review meeting
Take out 'Message counter reset' into a seperate store method
Implement Slot recovery after server shutdown
Code comment improvement and clustering enabled check moved outside of lock.
Remove slot associations during purge
Adding javadoc comments
Removing unused properties from MsgData
Remove slots in nodes only if in clustering mode
Merge pull request #166 from hastef88/queue_purge_feature_hector_support

Queue purge further refactoring - adding context to logs, missing comments
Merge pull request #164 from a5anka/slot_recovery

Implement Slot recovery after server shutdown
Non acknowledged message counter moved to OnFlightMessageTracker

Non acknowledged message tracking was previously done in AMQChannel. This tracking was
internally used by Andes for message delivery. This leads to non acknowledged message tracking
logic to be tightly coupled with Qpid implementation.

Fixed this by moving the non acknowledged message tracking logic to OnFlightMessageTracker.

Decrementing non acknowledge message count is moved into acknowledgement handling logic to avoid decrementing
count before disruptor handling the acknowledgement event.
Merge pull request #169 from Asitha/unacked-tracking

Non acknowledged message counter moved to OnFlightMessageTracker
Code Cleanup :construction_worker:

- Code comment issues fixed
- Unused imports variables removed.
Merge pull request #171 from Asitha/code-cleanup

Code Cleanup :construction_worker:
Replace SequentialThreadPoolExecuter with DistruptorBasedFlusher
Queue Entry convertion separated to a handler
Remove unnecessary releaseAllMessagesOfSlotFromTracking call
Implement message content caching in the deliver disruptor