new application stuff very hype (#1764)

* application stuff, more to come

* docstrings

* Update Message.js

src/structures/Message.js

@@ -3,6 +3,7 @@ const Attachment = require('./MessageAttachment');
 const Embed = require('./MessageEmbed');
 const MessageReaction = require('./MessageReaction');
 const ReactionCollector = require('./ReactionCollector');
+const ClientApplication = require('./ClientApplication');
 const Util = require('../util/Util');
 const Collection = require('../util/Collection');
 const Constants = require('../util/Constants');
@@ -137,6 +138,21 @@ class Message {
      */
     this.webhookID = data.webhook_id || null;
 
+    /**
+     * Supplimental application information for group activities
+     * @type {?ClientApplication}
+     */
+    this.application = data.application ? new ClientApplication(this.client, data.application) : null;
+
+    /**
+     * Group activity
+     * @type {?Object}
+     */
+    this.activiy = data.activity ? {
+      partyID: data.activity.party_id,
+      type: data.activity.type,
+    } : null;
+
     /**
      * Whether this message is a hit in a search
      * @type {?boolean}