notice new/deleted files and update the browser

I think this mostly boils down to `gulp.watch` being not nearly as awesome as `gulp-watch`. I messily fixed this in our fork [1], but you'll probably want to keep the separation of config and tasks somehow (or not; I certainly didn't feel the need to do so).

[1] - https://github.com/cloudfour/veelo-patterns/pull/4/commits/50a4b972c38b5fc9a6ce5f71f5c6baf76250b300