Added status fields to the progress widget.

Added a percent done and time left fields to the progress bar.

Added sprintf library to add in formatting.

Added testing for the task progress widget by adding some internal testing endpoints.  I'm also pulling in another node module (eventsource).
Switch the node module for eventsource to event-source to see if Travis is happier with that one.
Failed to commit a file.
Added a flag to make estimated time optional.
Merge pull request #572 from girder/progress-status

Added status fields to the progress widget.