Adds `model` option for `route#render`

Prior to this commit, one needs to set the `model` explicitly on the other controller using `controllerFor` (while trying to render a different template with `renderTemplate#render`)

    App.BioController = Em.ObjectController.extend();

    App.HomeRoute = Em.Route.extend({
      renderTemplate: function(){
        this.controllerFor('bio').set('content', model);
        this.render('bio');
      }
    });

This commit provides an option to set the `model` that will set to the non-route-generated `controller's` content after the controller has been looked-up

    App.HomeRoute = Em.Route.extend({
      renderTemplate: function(){          
        this.render('bio', {
          model: model
        });
      }
    });

Fixes #3796