add push notification subscription model

lib/model/pushnotificationsub.js

@@ -0,0 +1,32 @@
+'use strict';
+
+function PushNotificationSub() {};
+
+PushNotificationSub.create = function(opts) {
+  opts = opts || {};
+
+  var x = new PushNotificationSub();
+
+  x.version = '1.0.0';
+  x.createdOn = Math.floor(Date.now() / 1000);
+  x.copayerId = opts.copayerId;
+  x.token = opts.token;
+  x.packageName = opts.packageName;
+  x.platform = opts.platform;
+  return x;
+};
+
+PushNotificationSub.fromObj = function(obj) {
+  var x = new PushNotificationSub();
+
+  x.version = obj.version;
+  x.createdOn = obj.createdOn;
+  x.copayerId = obj.copayerId;
+  x.token = obj.token;
+  x.packageName = obj.packageName;
+  x.platform = obj.platform;
+  return x;
+};
+
+
+module.exports = PushNotificationSub;