Observer counter

[toydotgame]

New observer tracker like this:

let runningObservers = {
	"schedule": 0,      // schedule() observers
	"continuous": false // Indefinite observers from replace.js
};

Count up every time a new observer is launched, then decrement when closing the observer. That way, when the observer == 0 after Old Google writes these:

We can come back and say that Old Google is done! (Obviously runningObservers.continous permitting, of course)

(+obviously a rework of the current logic that determines if we need to print that warn or not)