#6581: Possibility to omit container tag for BaseListView and derivative...

https://github.com/yiisoft/yii2/issues/6581
Now there is a possibility to omit an item container class for yii\widgets\ListView by setting [itemOptions['tag']=>false] while running the widget.
But there is no ability to skip the wrapper of whole widget - it's always set to div, if undefined. 
I suggest a little improvement that allows to omit container tag by setting the [options['tag']=>false] like it's done with items of ListView.