message: Returned null if state's unchanged
  The prevState didn't get rest = true even after set to true in clearScene. Worked around by only updating state if scene's changed. Weirdly, it seems to get rest = true after this change!?
diff: @@ -30,7 +30,7 @@ class NavigationMotion extends React.Component<NavigationMotionProps, Navigation
  }
  static getDerivedStateFromProps({stateNavigator}, prevState) {
  var scene = stateNavigator.stateContext.crumbs.length;
  - return {scene, rest: prevState.scene === scene && prevState.rest};
  + return prevState.scene !== scene ? {scene, rest: false} : null;
  }
  getSharedElements(crumbs, oldUrl) {
  if (oldUrl === null || crumbs.length === oldUrl.split('crumb=').length - 1)
  