Add a "Pop Screen Out" functionality like Zeplin

Since the previous feature request was ignored and archived, I'm creating a new one.

As a developer many of us miss the “Pop Screen Out” feature of Zeplin which helps enourmously when finetuning the design of web and mobile app pages.

I’ve seen the Ghost Screen plugin, but it’s not as helpful as the freely positionable “Pop Screen Out” window.

Please add support for this - a proper Dev mode.