Add option to wlr/workspaces to sort workspaces by number

[herlev]

#1691 didn't work for me. This pull request fixes #1596, by adding the option "sort-by-number" to wlr/workspaces, which takes precedence over any other sort-by option if set to true.

Example config

"wlr/workspaces": {
  "sort-by-number": true,
}

The icons can still be changed using

"format-icons": {
  "1": "a",
  "2": "b",
  "3": "c",
  "urgent": "d",
  "active": "e",
  "default": "f"
}

and the sorting will still be done according to the actual workspace numbers.

[Alexays]

Thanks!
Can you update the man to add the change and also update the Github wiki? :)

[herlev]

I have updated both the man page and the wiki now.