[Enhancement] Open DOM inspector from Element Picker

[Mikey1993]

A button, which will open the DOM inspector (in a separate window?), within the Element Picker.
It fits there nicely.

It will also make the DOM inspector more usable and discoverable for new users.

[gorhill]

As per https://github.com/gorhill/uBlock/blob/master/CONTRIBUTING.md: "Submit feature requests" -- even more so for new landed features.