A detector to add "swipe to go back" functionality in custom routes or non cupertino routes.
- child: is the child to wrap with the pop gesture detector
- cutoffVelocity: is the minimum velocity needed for the gesture to trigger
- swipeAreaWidth: is the width of the detection area
- verticalPadding: allows to restrict the detection area remaining vertically centered
- popValue: is the value you want to pop out when performing a gesture