Layout

With a conf like this:

```coffeescript
testConf = 
    dataSource: 'sample_data/ego1.json'
    nodeOverlap: 10
    nodeRadius: 5
    fixRootNodes: true
```

We can achieve a layout like this:
![image](https://cloud.githubusercontent.com/assets/1875033/3395013/bf107012-fcf3-11e3-9d11-72dadc482b8b.png)

The k, gravity and link distance functions work...  However, with the collision detection functions working as a function of node size and the force layout of the graph constrained by the height and width of the graph - the graph will not layout correctly.