Push scalability (#3080)

* Update status through increment
* adds support for incrementing nested keys
* fix issue when having spaces in keys for ordering
* Refactors PushController to use worker
* Adds tests for custom push queue config
* Makes PushController adapter independant
* Better logging of _PushStatus in VERBOSE

src/ParseMessageQueue.js

@@ -0,0 +1,26 @@
+import { loadAdapter } from './Adapters/AdapterLoader';
+import {
+  EventEmitterMQ
+} from './Adapters/MessageQueue/EventEmitterMQ';
+
+const ParseMessageQueue = {};
+
+ParseMessageQueue.createPublisher = function(config: any): any {
+  const adapter = loadAdapter(config.messageQueueAdapter, EventEmitterMQ, config);
+  if (typeof adapter.createPublisher !== 'function') {
+    throw 'pubSubAdapter should have createPublisher()';
+  }
+  return adapter.createPublisher(config);
+}
+
+ParseMessageQueue.createSubscriber = function(config: any): void {
+  const adapter = loadAdapter(config.messageQueueAdapter, EventEmitterMQ, config)
+  if (typeof adapter.createSubscriber !== 'function') {
+    throw 'messageQueueAdapter should have createSubscriber()';
+  }
+  return adapter.createSubscriber(config);
+}
+
+export {
+  ParseMessageQueue
+}