Moving Facade::$app to Application::$Current

I really like the Facades construct, because it simplifies a call to a singleton, static instance of a Class.

I moved the Facade::$app to
```php

class Application extends Container implements HttpKernelInterface {

	/**
	 * Singleton instance
	 */
	private static $Current = null;
  
	/**
	 * Facade function: Get instance of Application
         * Set instance of Application, returns old instance
	 *
	 * @param Application  $newCurrent = null
	 * @return Application
	 */
	public static function Current($newCurrent = null) {
		$current = static::$Current;
    
		if ($newCurrent !== null) {
			// Force this to be only in testing environment?
			static::$Current = $newCurrent;
		}

		return $current;  // return only current or the old current
	}
```
The Current() function is also the heart of the new Facade class:
```php
namespace Illuminate\Support\Facades;

abstract class Facade {
	
	/**
	 * Facade function for a Singleton, or registered component
	 */
	public static function Current() {
		throw new \RuntimeException("Facade does not implement Current method.");
	}
	
	/**
	 * Handle dynamic, static calls to the Current() object.
	 *
	 * @param  string  $method
	 * @param  array   $args
	 * @return mixed
	 */
	public static function __callStatic($method, $args)
	{
		return call_user_func_array(array(static::Current(), $method), $args);
	}

}
```

Now for example, in the Illuminate\Support\Facades\Router class you see, that the functions become direct aliases:

```php
class Route extends Facade {

	// ...

	/**
	 * Determine if the current route uses a given controller action.
	 *
	 * @param  string  $action
	 * @return bool
	 */
	public static function uses($action)
	{
		return static::currentRouteUses($action);
	// instead of
	//	return static::$app->currentRouteUses($action);
	}

	/**
	 * Get the registered component 'router'.
	 *
	 * @return Illuminate\Routing\Router
	 */
	public static function Current() {
		return Illuminate\Foundation\Application::Current()['router'];
	}
}
```