jidejs/ui/bind should update on animation frame

[pago]

In order to prevent useless updates of the DOM, it would be favorable if jidejs/ui/bind scheduled its updates on the browser render loop (using requestAnimationFrame).

This will require a few changes to Observable.computed to allow manual dependency management in addition to the automatic one (we need to calculate dependencies in an async callback).

[pago]

Turns out that there wasn't really much to change after all. By making the binding observable lazy, we make sure it is only ever computed (and its dependencies reevaluated) when we need to. Thus, we just need to delay that to the animation frame (using subscribe).

I'm leaving this open to expand it to the foreach binding where we need to buffer the changes of the ObservableList.