further refactoring - adding context to logs, missing comments
improvements as per peer reveiews
Merge pull request #167 from pamod/mqtt_dev

MQTT Perf Enhancements
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.
initial commit of new configuration access logic

1. Introduced new configuration manager class (singleton) based on apache commons composite configurations to load the config files during initialization
2. New configuration properties and their default values are maintained as enums.
3. qpid configuration classes were moved to "org.wso2.andes.configuration.qpid" from "org.wso2.andes.server.configuration"
4. MQTT configurations moved into andes config file
5. Added "commons-jxpath" since it is required by "commons-configuration" to handle xpath queries.
6. Added meaningful comments to describe properties and their usage.

Conflicts:
	modules/andes-core/broker/src/main/java/org/wso2/andes/kernel/AndesKernelBoot.java
	modules/andes-core/broker/src/main/java/org/wso2/andes/server/slot/SlotDeliveryWorkerManager.java
Change qpid config files namespace to "org.wso2.andes.configuration.qpid" instead of "org.wso2.andes.configuration.qpid.configuration"

Initialize AndesConfigurationManager at the QpidServiceComponent bundle activate event.

Log exception that occurs when retrieving configurations, even though the default value is applied.
Merge pull request #169 from Asitha/unacked-tracking

Non acknowledged message counter moved to OnFlightMessageTracker
Added missing license header
Code Cleanup :construction_worker:

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

Code Cleanup :construction_worker:
Merge pull request #170 from hastef88/configuration_revamp_m2

Configuration revamp m2
Refactoring as per peer reviews and fix issue coming from conflict resolution