Provide default $_SESSION array superglobal proxy storage adapter

## Overview
The Session Storage classes currently replace the $_SESSION superglobal with an ArrayObject.  This is fine and dandy until you need to incorporate third party libraries.  This is due to a bug in PHP which does not allow offsetGet to return a reference (ArrayObject only).  This causes an error when attempting to unset a multi-dimensional array.

This new storage adapter will *be the default* and will have a slight break in BC.  The new storage adapter implements ArrayAccess and proxies to the $_SESSION container.  The BC break only happens when manipulating the storage object directly; however, this is generally more limited to a type cast such as: $array = (array) $session->storage; as it has been implemented with ArrayAccess and utilizing magic methods to incorporate much of the prior behavior.

### Utilizing the Previous Storage:
```php
$sessionManager = new SessionManager(
    new Zend\Session\Config\SessionConfig(),
    new Zend\Session\Storage\SessionStorage()
);
```