Basic Flow Visualization

I've added some basic flow visualization working off some existing code (see 7da113465ac15e5a7e24241abfed03806239404f). 

Here's a screenshot of how it looks. Please let me know if there are any necessary changes to get this pulled. I'll be happy to help.

In progress build:
![screenshot](https://f.cloud.github.com/assets/42138/143157/a5f112b6-7375-11e2-88ab-00225947fe58.png)

Finished build:
![screenshot](https://f.cloud.github.com/assets/42138/143154/88bd96b6-7374-11e2-96e1-9fa72b3c6a3c.png)



It's using the latest version of jsPlumb - really only to draw the arrows between builds. Right now the builds are just drawn in a <ul> and the child <li>'s are floated:left to create a type of grid, so longer builds will just wrap on the screen. Ideally there would be a better way of rendering them (maybe so they always go horizontal), but that may be for another pull request. 

I had to add the FlowListener to keep track of when a build is started/completed. scheduleBuild2 only gives a future that returns when a build is complete, and I wanted to be able to show builds that are in progress.