Create a request object to replace magic args

Replacing the `_method`, `_route`, etc parameters that we had is something we need to do for 2.0.

Here's one idea to get the ball rolling: let's look at Symfony's [HttpFoundation\Request](http://api.symfony.com/2.5/Symfony/Component/HttpFoundation/Request.html). However, let's merge it with the args passing by using ArrayAccess.

Thoughts on that?
