Summary: public
The gesture that moves scene around should only be attached when the
move starts at the moment that the first move is granted.
No move would ever be granted if the move event is prevented by the
decendent children (e.g. a slider component).
For now, the move gesture is attached at `onPanResponderGrant`
instead of `onPanResponderMove` thus we'd create "ghost-move-gesture"
when no actual moves is received my the navigator.
Reviewed By: fkgozali
Differential Revision: D2683802
fb-gh-sync-id: 50ae877787167511df48378304bd2ad665c73300
e0d53e1c48