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.
Added missing license header
Merge pull request #170 from hastef88/configuration_revamp_m2

Configuration revamp m2
Refactoring as per peer reviews and fix issue coming from conflict resolution
Merge pull request #172 from hastef88/configuration_peer_review_refactor

Refactoring as per peer reviews and fix issue coming from conflict resolution
performance related changes and some NPE fixed
Merge pull request #173 from indikasampath2000/performance

performance related changes and some NPE fixed
MQTT Performance improvements, Attending to TODOs
Merge pull request #174 from pamod/mqtt_dev

MQTT Performance improvements, Attending to TODOs
MQTT fixing some loggging issues
Merge pull request #175 from pamod/mqtt_dev

MQTT fixing some loggging issues
Replace SequentialThreadPoolExecuter with DistruptorBasedFlusher
Queue Entry convertion separated to a handler
Implement message content caching in the deliver disruptor
Add exception handler
Change delivery code package name
Change local subscription API to use AndesContent