Merge pull request #96 from gzhangT/master

Added a column to display a job's start and end time.
Rescaled the edges based on hdfs_written.
Added some comments.
Tweak the table text: "10 mins, 53 sec" -> "10m 53s".
Fixes based on the review.
Removed unnecessary commas.
Reset the view to rescale edges after each update.
Modified event.json to demo vector scaling change.
Factored out the function for rescale edges.
Modified the event.json data to make the vector rescaling look better since changed the max width to 16px.
Speed up the progress by moving all the PPNL calls to a separate thread.