Summary:
Fix a bug in NavigationScenesReducer that prevents scenes from re-rendering.
This happens when jumping the index between routes.
The fix is to add an new property `isActive` to `NavigationScene` to indicate the current active scene.
Reviewed By: ericvicenti
Differential Revision: D3479736
fbshipit-source-id: a71419887acd94ad2fead71596ca46419a88efef