Feature/toolbar ui 2

continued from https://github.com/yiisoft/yii2/pull/2320 discussion...

* @samdark the **home icon** could be handled just by a custom panel - maybe this will suit everyone?
* instead of `panelsPosition` we could also introduce a `position` property
* how to use `&nbsp;` in the date formatter?
* the toolbar on the debug module index view is a bit inconsistent with the other views