Fix config.json and add favicon support

/to @bajtos or @ritch 

The PR fixes 3 issues:
- Make sure the app is listening on 0.0.0.0:3000 instead of localhost:3000
- Add favicon middleware to avoid 404 warnings
- Fixes https://github.com/strongloop/generator-loopback/issues/12
> If you're suggesting there's a way we can listen on 0.0.0.0 without breaking Windows, that would be ideal.

To my best knowledge, when you don't specify any host at all (i.e. `host: undefined`), the server will listen on all interfaces even on Windows. Then in the loopback `listening` handler, the code building the server URL will use `localhost` when no host is defined.

I am saying there are two options how to listen on all interfaces AND have a Windows-friendly URL:

```js
// Option A - specify the URL too
{ name: 'host': value: '0.0.0.0' }
{ name: 'port', value: 3000 },
{ name: 'url', value: 'http://localhost:3000/' }

// Option B - use defaults
{ name: 'port', value: '3000' }
// no host, no url
// the port can be actually omitted too, but whatever
```

> If it is a choice between confusing Windows users and having the app not work when deployed to a server.. sucks to be a Windows user.

Well, I would hope people are careful about what interfaces their app listens on the server. In many cases the app runs behind a reverse proxy like nginx, so it is in fact desirable to listen on localhost only. Also the value scaffolded by workspace is the configuration for the development environment, where it is may be better to listen on `localhost` only.

As for confusing Windows users - the previous version of sls-sample-app used to print `http://0.0.0.0:3000` URL and we had to change it because it was confusing users.

Anyways, this discussion is academic, it is possible to have both - an app listening on all interfaces and a URL that works on Windows too.