more information in event.log for JOB_DONE
support job recompute API: PUT /job/<id>?recomput=<stage>, recompute a job from a given task stage
provide API to update clientgroup for a job (PUT /job/<id>?clientgroup=<newgroup>)
Merge pull request #90 from wtangiit/master

two more job manipulation APIs (recompute a workflow job from a given stage and updating the clientgroup)