Make "individual worskapaces per monitor" an option!

[Arntzzen]

Ref. commit #15655
I like having my two monitors share the workspaces and was sad when I found out that the with version 4.5, this is now changed to where each monitor has their own workspaces. I have my system to keep track of which monitor has which workspace and would therefore like the option to choose. Kind of tiresome to change this back myself.