added remove and removeAll methods and now growl message could be visibl...

For $.growl added remove and removeAll methods 

```javascript
var notice = $.growl.notice({
  message: 'Hello'
});

$.growl.remove(notice);
$.growl.removeAll();
```

And possibility not to hide notification until close button is clicked or remove/removeAll method is called.

```javascript
$.growl.notice({
  message: 'Hello',
  duration: false
});
```