Add support for notes (#860)

* Add support for notes

* Ensure consistency with notes from ready payload

* Add getter method for users

* Minor tweaks

* Update warning messages

* More minor fixes

src/client/actions/ActionsManager.js

@@ -21,6 +21,7 @@ class ActionsManager {
     this.register('GuildRoleUpdate');
     this.register('UserGet');
     this.register('UserUpdate');
+    this.register('UserNoteUpdate');
     this.register('GuildSync');
     this.register('GuildEmojiCreate');
     this.register('GuildEmojiDelete');