juwang - adding id for TaskMessage

TaskMessage in Java contains both message and taskid, currently in the bridge, only message is available.  This PR added task id in the TaskMessageBridge, made it available in RunningTaskClrJava so that it can be accessed by TaskMessage  at C# side cross the bridge. 

The PR also optimized RunningTaskClr2Java to get id cross the bridge only once in the constructor and store it in the object. It will be returned whenever GetId is called. 
need to add this:

_jstringId = reinterpret_cast<jstring>(env->NewGlobalRef(_jstringId ));