Grunt v2

This is an update of the Grunt workflow that should solve some problems.

- Remove shell script
- Use nodemon for restarting the server, grunt-contrib-watch for compiling stylus files
- Update README.md (please check for english!)

Locally just run `grunt run:dev` to have the server restarting automatically & stylus files to be compiled when they change.

In production, I leave this to @lefnire but I don't think that running grunt-contrib-watch to recompile stylus & js is anything useful on Heroku since the app is restarted when new code is pushed. I understand using `nodemon` in case the server crash to restart it.

So I would advise using this command on Heroku:

`grunt build:prod && grunt nodemon` so that the assets are built only once but the server restarts in case it crashed.