Modification for publishing events to indicate artifact deployment status.

- The modification were done, due to the requirements of WSO2-AppFactory product.
- Introduced new two events to indicate 'artifact deployment started' and 'artifact deployment completed'  points.
- Cartridge agent was modified to get updated artifacts with their last modified time in the repository.
- Cartridge agent was modified to publish new events to message broker.
- Messaging component was modified to process new two event types. (Introduced few new classes to match the existing pattern of the code)
Error handling here should be done properly here, when catching an exception, the "gitOperationResult" object state is not changed in any way, to signal an error condition to the caller. And if this is not done, and ignored, most probably, the caller of this is also not handling an error state from that object, all aspects of this has to be checked.