introduce single active scratchpad hook

[philib]

Description

I added a logHook that ensures that only the most recent scratchpad is active on the workspace at any given time. When opening a new scratchpad, the previous scratchpad is moved to the corresponding scratchpad workspace.

Motivation: I use floating scratchpad to open terminals, notes, etc. quickly. Since nsHideOnFocusLoss hides scratchpad more often, then i intended to, the scratchpads can pile up very fast, which leads to the fact that I have to "dismantle" the stack of scratchpads manually. To prevent this, I now use this logHook. I thought I'd share it in case anyone has a similar workflow and is also interested.

I am a Haskell beginner, so please bear with me. I would be glad about feedback.

Checklist

• I've read CONTRIBUTING.md

• I've considered how to best test these changes (property, unit,
  manually, ...) and concluded: manually tested

• I updated the CHANGES.md file

[slotThe]

Thank you for the contribution! May I ask how this is different from nsHideOnFocusLoss? To me, it seems that

only the most recent scratchpad is active on the workspace at any given time. When opening a new scratchpad, the previous scratchpad is moved to the corresponding scratchpad workspace.

is describing exactly the same functionality

EDIT: Ah, I guess the motive is different—one might well want the scratchpad to stay when it looses focus, as long as only one is on the current workspace. Ignore me :)

[slotThe]

Thank you for the contribution 🎉