Handle edge tap decisions in app

[chocolatkey]

Edge taps to turn pages should be handled in the (test) app. The navigator will just send the tap event.

Each app might want different edge threshold, or even disable this feature for accessibility reasons.

Originally posted by @mickael-menu in #12 (comment)

[JayPanoz]

This is resurfacing so some additional context.

Right now the default listener for both tap and click is allocating one quarter of the iframe window on the left and the right to navigate to the previous/next screen. It is relying on cframes to access the window.innerWidth, a property we want to make private eventually.

cc @HadrienGardeur in case you want to develop further.