Graph display tweaks

As mentioned in the commits, there are two changes here:

1) Add highlighting when hovering on legend items
![preview](https://f.cloud.github.com/assets/193/368642/e2ae1464-a2c4-11e2-997f-5faa48df3b4e.png)

2) Applies some basic styling to the timeseries tooltips to ensure they fit on the screen. ![preview](https://f.cloud.github.com/assets/193/368644/f180f75e-a2c4-11e2-8759-457b255bdfcf.png)