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');

// Initialise a request
var req = http('http://www.naver.com');

// Set headers
req = req.withHeaders({'hello': 'world'});

// Set the body
req = req.withJSON({'hello': 'world'}); // Set with JSON
req = req.withForm({'hello': 'world'}); // Set with form data

// Set the query string
req = req.withQueryString({'hello': 'world'}); // which could surely be set with URL
// Same with http://www.naver.com/?hello=world

// Auth
req = req.withAuth('someusername', 'somepassword'); // basic auth
req = req.withAuth('someusername', 'somepassword', 'digest'); // specify auth scheme

// Send request
var future = req.post(); // Also support `get`, `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
});
```