Correctly handle mouse event submission

[uuf6429]

Right now there is a general issue with dispatching mouse events; it's done asynchronously via RemoteDebug and the callback handler is called when the event is sent, not received and processed.

Hence in some cases, for example, we fail to properly detect page state (like navigation).

A possible solution is to bind a mouse handler to the affected element that sets the execution response, instead of relying on the callback handler.