Add Gruntfile.js to bedrock

Let's try and improve our front-end development workflow on bedrock...

This PR includes a basic [Grunt](http://gruntjs.com/) file to help automate the following tasks:

* Starting the local bedrock server.
* Compiling CSS when a LESS file changes (no more reloading the page twice, yay!).
* Running JSHint when a JavaScript file changes.
* Live reloading in the browser whenever an HTML, CSS of JavaScript file changes.

There's probably more stuff we can build on, but this is a start at least for discussion/testing. This PR leaves using Grunt as totally optional, so it doesn't make getting set up on bedrock and more difficult. It is just there for those who may want to try using it.