Add an Android-like screenshot button to the workspaces view

## Problem
Sometimes people feel that they want a UI way of screenshotting, that wouldn't require them to open a seperate app.

## Proposal
Add a screenshot button to the workspaces overview, possibly as a small round bubble in a corner of the worspace preview (like the notification dissmiss one)

## Prior Art
Maybe something like this, but with a more suitable and visible icon