Separate status request from client

Try with a different approach.

With the DiC support the usage is more simple:

```php
<?php
$status = new Status("gianarb", "gstatus");
$status->setStatusFor("1ab5f09eb4e736890b17b7abdb80ed3e368a478f", [
    "state" =>  "failure",
    "target_url" => "http://gianarb.it",
    "description" => "D'oh!",
    "context" => "my/test",
]);

$client = $container->get("github.client")
    ->send($status);
```
Too much responsibilities for this class:
  * http client
  * request
  * github statuses