Add ScriptableHttp.

ScriptableHttp is the module to send HTTP request from the Beyond
plugin. Basically, it's the thin wrapper for Play's WS API.

Surely I'll update the Wiki later, but now I'll share the basic usage here.

```javascript
var http = require('http');
var req = http('http://www.naver.com');
req = req.withHeaders({'hello': 'world'});
req = req.withJSON({'hello': 'world'}); // Set JSON body
req = req.withForm({'hello': 'world'}); // Set form body
req = req.withQueryString({'hello': 'world'}); // Set query string, which could be done with URL
var future = req.get(); // Also support `put`, `head`, `put`, `delete`, `options`, `patch`
future.onSuccess(function (res) {
  console.log(res.status); // Int
  console.log(res.statusText); // String
  console.log(res.body); // body text: String
  console.log(JSON.stringify(res.headers)); // headers as object
});
```