Avoid $_POST direct use

Summary:
Frameworks like Laravel offers wrappers around superglobals.

It allows a more versatile code (but $_REQUEST would do too),
and some sanitization.

Test Plan:
(1) Capture a request (for example through Runscope) with this code:

protected function extractPayload () {
	$this->payload = $_POST;
	print_r($_POST);
	abort(503, "Debugging payload");
}

(2) Replace by $this->payload = Request::all();.

(3) Replay the request, and check if the reply diff is identical

Reviewers: dereckson

Differential Revision: http://devcentral.nasqueron.org/D119