Version args

I added a few lines to allow to add a versioned files in the config file.
You can add a property "versionArgs" in your config files in this way
```
"versionArgs" : {
  'js/lib/mylib.js': 2,
  'js/lib/other.js': 5
}
```

When the file 'js/lib/mylib.js' will be request it will be 'protocol://host:port/js/lib/mylib?v_arg=2'. In this way the file will be cached in the browser until the version '2' changes.