Use grunt-contrib-watch for livereload

https://github.com/gruntjs/grunt-contrib-watch#live-reloading

grunt-contrib-watch got support for livereload. We should convert all generators over to it asap.

<del>This is just a start as I was stopped by a potential [bug](https://github.com/intesso/connect-livereload/issues/1) in connect-livereload. @kevva @passy would you be able to look into it?</del>