Move build system to Grunt

**Please don't merge this yet. I'm opening this early so that we can discuss things as we go.**

[Grunt](http://gruntjs.com/) is a build system written in Javascript for building things with web technologies. It has official support for JSHint, RequireJS, and SASS. As it shells out to native Javascript (via node/V8) and Ruby VMs for everything, it is *way* faster than our maven build system, but may be more difficult to install and configure on Windows machines.

![Selection_001](https://f.cloud.github.com/assets/180404/418069/d204003e-ac8c-11e2-8405-e0452199aefe.png)