Dependency Graphing Command

Hi,
This pull request adds the functionality to composer to graph dependencies. It adds a new composer command, 'graph', which generates an HTML page at the specified path with a D3js powered adjacency matrix style graph.

![Screenshot](https://f.cloud.github.com/assets/485941/39509/947b0984-552e-11e2-942e-38e0f72f8ee6.png)