open(userId = null, focusInput = false) {
        this.initChannel(userId).then(messages => {
            const channelCurrentUser = this.getChannelCurrentUser();
            this.UI.openBlockAndAppendMessages(messages, channelCurrentUser, focusInput);
            this.Events.addIntervalCheckForMessages(this.checkForNewMessages.bind(this));
            this.Events.addBlockCloseEvent(this.close.bind(this));
            this.Events.addMessageEvent(this.sendMessageToCurrentUser.bind(this));
            this.Events.addLoadOlderMessagesEvent(this.loadOlderMessages.bind(this));
        });
    }
Shows PM window,
Initializes new PM channel, receives last messages between both users
Renders messages into window

@param userId
@param focusInput