Dragging workspace out of window to open it in a new window

[TheTrueWhiteOwl]

Discussion #4496 made me start thinking about more interactions with the workspace icon strip.

I propose being able to drag from one of the workspace icons to open all of the tabs currently open within it in a new window (removing them from the old window so that they aren't just being duplicated). This behaviour is inspired on the behaviour of dragging a tab out of the window to open it in a new window.

If the workspace being dragged into a new window is the current workspace, then the current window will switch to the last used workspace with tabs open inside of it. (this means that regardless of which workspace you drag and drop, after performing this action you are always left with two browser windows, each on a different workspace).