Create general notification system for out-game events such as loading and saving

[v79]

Also for next turn calculations.

Next turn is essentially instant, but may still be useful to show some sort of UI to indicate progress.

• A notification/progress bar just above the bottom of the screen, on top of the cards
• Updates on signals sent
• Disappears when the turn starts
• Needs to be able to display text, a progress bar, or both

I can't call it notifications, that name is taken. Toast?

[v79]

I've got completely stuck trying to implement a delay that will pause the processing of the game, which I am trying to do to force a delay.
I wanted something like:

fun nextTurn() {
  godotCoroutine {
    signalBus.toast.emit("Message")
    signalBus.toastExpired.await()
   doThings()
  }
}

But I've got threading problems.