Merge pull request #42 from sajinidesilva/slots_Imp

Slots Implementation v1
Deprecated MessageStore implementations removed

	deleted:    modules/andes-core/broker/src/main/java/org/wso2/andes/messageStore/CassandraBasedMessageStoreImpl.java
	deleted:    modules/andes-core/broker/src/main/java/org/wso2/andes/messageStore/InMemoryMessageStore.java
Storage related classes moved to org.wso2.andes.store package
Merge pull request #43 from Asitha/storage-restructure

Storage restructure
refactored the slot imlementation code