[WDT] Show text description of HTTP Status Code in WDT

As the title says. Didn't seem like a good idea to collect these static, unchanging strings via `RequestDataCollector`, so I created a Twig filter.

![Screen Shot 2013-01-10 at 14 54 25](https://f.cloud.github.com/assets/363540/56964/50c2dea2-5b36-11e2-959a-8a3e299c2bd0.png)