Fix annotation pages

cf410d0 broke standalone annotation pages by changing
`threadRoot.children` from an array into a thread container.
Unsurprisingly, `children` is supposed to be an array.

h/static/scripts/annotation-viewer-controller.coffee

@@ -26,7 +26,7 @@ module.exports = class AnnotationViewerController
 
     store.AnnotationResource.read id: id, (annotation) ->
       annotationMapper.loadAnnotations([annotation])
-      $scope.threadRoot = {children: threading.idTable[id]}
+      $scope.threadRoot = {children: [threading.idTable[id]]}
     store.SearchResource.get references: id, ({rows}) ->
       annotationMapper.loadAnnotations(rows)