Redesign HTML report

Platforms collapsed
![screen shot 2014-10-23 at 6 06 55 pm](https://cloud.githubusercontent.com/assets/1043291/4763958/e0c099f0-5b1a-11e4-98ec-05e8a5ffda08.png)

No differences
![screen shot 2014-10-23 at 6 07 29 pm](https://cloud.githubusercontent.com/assets/1043291/4763956/e082c81e-5b1a-11e4-8d36-95f12d7759d2.png)

Missing images
![screen shot 2014-10-23 at 6 07 14 pm](https://cloud.githubusercontent.com/assets/1043291/4763957/e0c083c0-5b1a-11e4-9582-80ae8af8d342.png)

Diff overlaid, 2 up
![screen shot 2014-10-23 at 6 08 16 pm](https://cloud.githubusercontent.com/assets/1043291/4763955/e0bd0e5c-5b1a-11e4-95b4-d2ebfa0911bf.png)

1 up
![screen shot 2014-10-23 at 6 14 43 pm](https://cloud.githubusercontent.com/assets/1043291/4763967/337a3a20-5b1b-11e4-9d54-72ba7109a576.png)