camel-jetty - added option to quickly enable CORS

While connecting to a jetty endpoint from a development web server running on a different port, AJAX calls, fail due to CORS restrictions. 

See: https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS


camel-jetty component can be already be configured providing a list of Filters with:

```java
       List<Filter> list = new ArrayList<Filter>() ;
        list.add(new org.eclipse.jetty.servlets.CrossOriginFilter());
```

and using already existing `filtersRef` option.

The code in the PR adds a simpler boolean option that enables just the CORS filter, for quicker access of the functionality, ideal for development time.