modules should be restructured to allow extensions

[a5anka]

I propose the following module restructuring to manage multiple coordination strategy implementations effectively.

List of modules,

• org.wso2.carbon.cluster.coordinator.core - This will include the core logic independent of the coordination strategy implementation. This will use a configuration to select between the available CoordinationStrategy implementations. An OSGI service implementation can be used to indicate the availability of the component.
• org.wso2.carbon.cluster.coordinator.rdbms - This component will provide the rdbms based implementation as a OSGi service
• org.wso2.carbon.cluster.coordinator.zookeeper - This component will provide the ZooKeeper based implementation as a OSGi service

[a5anka]

Part of the implementation is done in #28. Tasks left to do are,

• Using a configuration to select a coordination strategy when multiple implementations are available in the OSGI environment.
• Packing the config with feature (not directly related to the feature)