Juwang-Add RunningTask event handler, bridge classes and methods

When running task event is received from an Evaluator, it will trigger the call at RunningTask Event Handler registered at Java side. We would like to propagate the event to C# cross the bridge so that C# client can have their RunningTask event handler so that to get the task information including the Active Context. 

This PR adds a Java RunningTask event handler, creates bridge classes and methods, handles the calls between Java and C#. 
I would suggest the Id be populated this in the construtor and keep it as a data member of the class, so that we do not need to invoke bridge call round trip everytime we need the running task id (which is probably quite frequent).