New "dial" view, similar to "gauge"

Displays a vector-based gauge on an HTML `<canvas>` element.

The commit message of 46a7f1f3 gives a bit more details. Here's a screenshot to give an idea of how it looks like:

![dial](https://cloud.githubusercontent.com/assets/37533/4242257/e4b31e24-39fb-11e4-8c0f-9b4163a3c274.png)