Added CORS support

This code works for me (tm)

To enable CORS support, add this to your config.json:

```
  "CORS": {
    "Origin": ["https://home.muse.net.nz:8000", "http://localhost", "http://www.number10.gov.uk:80"],,
    "Headers": ["DNT","X-Mx-ReqToken","Keep-Alive","User-Agent","X-Requested-With","If-Modified-Since","Cache-Control","Content-Type"],
    "MaxAge": "1728000"
  }
```

`Origin`, `Headers` and `MaxAge` all need to be defined. Use `"Origin":["*"]` to enable access from anywhere.