Added browser live reloading to Grunt

This comes with the latest version of [grunt's watch task](https://github.com/gruntjs/grunt-contrib-watch#live-reloading) (which is already referenced in package.json) and is pretty easy and straightforward to use. It only requires the [livereload browser plugin](https://github.com/gruntjs/grunt-contrib-watch#using-live-reload-with-the-browser-extension) or [adding a \<script\> tag](https://github.com/gruntjs/grunt-contrib-watch#enabling-live-reload-in-your-html). 

Also, I made it optional and disabled by default.