fix(focused-content): Prevent keydowns from outpacing animation frames, improves keyboard move speed through thread list

To reproduce previous issue, turn key rpeat speed all the way up and then hold an arrow key.

src/flux/stores/focused-content-store.coffee

@@ -81,6 +81,7 @@ class FocusedContentStore
     return if @_keyboardCursor[collection]?.id is item?.id
 
     @_keyboardCursor[collection] = item
+    window.requestAnimationFrame =>
       @trigger({ impactsCollection: (c) -> c is collection })
 
   _onFocus: ({collection, item}) =>
@@ -89,7 +90,7 @@ class FocusedContentStore
 
     @_focused[collection] = item
     @_keyboardCursor[collection] = item if item
-
+    window.requestAnimationFrame =>
       @trigger({ impactsCollection: (c) -> c is collection })
 
   _onWorkspaceChange: =>