Allow route middlewares to be grouped together

[winglian]

This will allow multiple middlewares to be packaged together under a single identifier. For example, if I wanted to move Illuminate\Session\Middleware\StartSession and Illuminate\View\Middleware\ShareErrorsFromSession from the global middlewares to the route middlewares, but keep them together so only routes that need sessions would only need to reference a single middleware.

    Route::group(['middleware' => ['session']], function() {
        // ...
    });

    protected $routeMiddleware = [
        'auth' => 'App\Http\Middleware\Authenticate',
        'auth.basic' => 'App\Auth\Middleware\AuthenticateWithBasicAuth',
        'guest' => 'App\Http\Middleware\RedirectIfAuthenticated',
        'session' => [
            'Illuminate\Session\Middleware\StartSession',
            'Illuminate\View\Middleware\ShareErrorsFromSession',
        ]
    ];

[GrahamCampbell]

Send to 5.0 please.