[RFR] Make the chart look nicer

* dim colors a bit
* fix bug resulting in absent tests and holes in the graph
* hide fastest tests (< 50 ms)
* sort by random to avoid visual pattern

![image](https://f.cloud.github.com/assets/99944/1463760/633d5fa4-4536-11e3-9824-362df4ab8c2c.png)