Adding files for Running Task Handler

This change is to add running task handlers in Java and set up a bridge
for C#.
Update gitignore file
add setMessage method in runningtask bridge
merge from reef-bridge
brisgde interface and methods for RunningTask
update for the JobDriver
address CR issues
adding getId for bridge to get RunningTask id
Merge pull request #887 from Microsoft-CISL/juwang-reef-bridge-runningtask

Juwang-Add RunningTask event handler, bridge classes and methods