feat: listen to group events (#90)

This allows you to listen for user joins or leaves, description updates, subject updates, picture updates, and group settings updates.

Co-authored-by: Pedro S. Lopez <pedroslopez@me.com>

src/util/Constants.js

@@ -36,6 +36,9 @@ exports.Events = {
     MESSAGE_REVOKED_EVERYONE: 'message_revoke_everyone',
     MESSAGE_REVOKED_ME: 'message_revoke_me',
     MESSAGE_ACK: 'message_ack',
+    GROUP_JOIN: 'group_join',
+    GROUP_LEAVE: 'group_leave',
+    GROUP_UPDATE: 'group_update',
     QR_RECEIVED: 'qr',
     DISCONNECTED: 'disconnected',
     STATE_CHANGED: 'change_state',
@@ -61,6 +64,23 @@ exports.MessageTypes = {
     UNKNOWN: 'unknown'
 };
 
+/**
+ * Group notification types
+ * @readonly
+ * @enum {string}
+ */
+exports.GroupNotificationTypes = {
+    ADD: 'add',
+    INVITE: 'invite',
+    REMOVE: 'remove',
+    LEAVE: 'leave',
+    SUBJECT: 'subject',
+    DESCRIPTION: 'description',
+    PICTURE: 'picture',
+    ANNOUNCE: 'announce',
+    RESTRICT: 'restrict',
+};
+
 /**
  * Chat types
  * @readonly