Issue #47: SMPP Server is not sending DLR's to clients

Implement the SmppServerConnector.process() method to handle DeliverSm and Delivery Receipts.
Add test to validate functionality.
Issue #48: Add support for MongoDB

Split the core-context.xml and use different files for each message
store.
Create a MongoMessageStore class.
Add some tests for the new MongoMessageStore.
Change the message id to an object instead of a long.
Fix some issues with the id change.
Increase SmppConnectorTest default timeout.

Sometimes it fails in Buildhive.