Make the CallbacksRegistry a separate module, though rather small.

common/api/lib/callbacks_registry.coffee

@@ -0,0 +1,21 @@
+module.exports =
+class CallbacksRegistry
+  constructor: ->
+    @nextId = 0
+    @callbacks = {}
+
+  add: (callback) ->
+    @callbacks[++@nextId] = callback
+    @nextId
+
+  get: (id) ->
+    @callbacks[id]
+
+  call: (id, args...) ->
+    @get(id).call global, args...
+
+  apply: (id, args...) ->
+    @get(id).apply global, args...
+
+  remove: (id) ->
+    delete @callbacks[id]