Dashboard rewrite (WIP)

This is still a WIP, please **do not merge** yet.

This is meant to replace the current etcd dashboard. It uses common coreos ui modules and styles from the coreos-web library, and should be easier to use and maintain.

The key/value browser is complete for now (see below) and code review is welcome. I'm still working on the stats page.

![screenshot 2014-04-11 10 38 50](https://cloud.githubusercontent.com/assets/224222/2682750/2d822c8c-c1a0-11e3-92e2-b3066774be1b.png)