Add basic CORS support 

This PR add basic support for CORS mechanism.

can be used through the programmatic API 

```java

server.configure(routes -> routes.
  options("/mycorsservice", context -> {
    if (context.isPreflight()) ...
    return new Payload("")
      .withCode(200)
      .withAllowOrigin("*")
      .withAllowCredentials(true)
      .withExposeHeaders("X-WHATEVER")
      .withMaxAge(3600);
  })
);

```

or the annotation based API

```java
public static class MyResource {
  @Options("/mycorsservice")
  @AllowOrigin("http://www.code-story.net")
  @AllowMethods({"GET", "POST"})
  @AllowHeaders("X-WHATEVER")
  public String myService() {
    return "";
  }
}
```