feat(SessionManager): New feature from Discord

src/client/Client.js

@@ -15,6 +15,7 @@ const ClientSettingManager = require('../managers/ClientSettingManager');
 const DeveloperPortalManager = require('../managers/DeveloperPortalManager');
 const GuildManager = require('../managers/GuildManager');
 const RelationshipsManager = require('../managers/RelationshipsManager');
+const SessionManager = require('../managers/SessionManager');
 const UserManager = require('../managers/UserManager');
 const VoiceStateManager = require('../managers/VoiceStateManager');
 const ShardClientUtil = require('../sharding/ShardClientUtil');
@@ -156,6 +157,12 @@ class Client extends BaseClient {
      */
     this.guilds = new GuildManager(this);
 
+    /**
+     * All of the sessions of the client
+     * @type {SessionManager}
+     */
+    this.sessions = new SessionManager(this);
+
     /**
      * All of the {@link Channel}s that the client is currently handling, mapped by their ids -
      * as long as sharding isn't being used, this will be *every* channel in *every* guild the bot