Promising concept for a dev-browser

… but still needs much work.

* no way to configure the amout of the preview panes
* no way to configure the widths of the preview panes
* no way to set the height for a mobile preview pane
* very sluggish performance when resizing window
* no way to bookmark a url

too expensive - interested users should wait.

tt-77 about Duo, v1.0