Pause gameplay while popups are visible

[balloonpopper]

Adds pausing functionality for when popups appear

Unpausing is done in each popup individually as I didn't want the animations in the room to be running until the fade completed, so the restart needed to be in each popup rather than a single call in popochiu_popup.gd

Known bugs that I haven't been able to fix (some help would be appreciated)

1. Character facing direction isn't corrected until after the game is unpaused. The fixes I've tried haven't worked.
2. If a character is walking when you save the game - e.g.

			await C.get_OfficerBrown().walk_to_marker("ExitPoint")

the character's walking state is not restored when you load the save. This appears to be a generic save-game bug, and not one in my code.