Stopwatch, an interactive stopwatch

Continued from duckduckgo/zeroclickinfo-goodies#329.

It's a stopwatch. Like someone said in the forum, it may be hard to decide on a good look & feel. Because of this, and for the testing of functionality, I put it up [here](http://mattr555.github.io/stopwatch.html). Feel free to play around with the CSS in-browser and tell me what you like.

I'm not sure how to manage both the split and the lap button; we may decide that we should only use one of them.

Finally, so I could test with DuckPAN, which doesn't support `call_type => 'self'`, I had to make it call to httpbin.org. I marked the lines that should change in production with comments, and @jagtalon has agreed to fix them when it's time to merge.

![image](https://f.cloud.github.com/assets/4411471/2189806/190be8a8-981d-11e3-83d3-b0b77c38f285.png)