Improve integration with Rocket Chat

A basic integration with Rocket Chat has been implemented in !366 (merged). We need following improvements:

1. Enable showing standard login page in Rocket Chat, instead of parking page coming from Condenser. This is needed for users running on mobile application. This implicates closing chat drawer and disabling chat button, when user is logged out in Rocket Chat.
2. Improve the way Rocket Chat handles logout in other browser's tab. This should be done in https://github.com/openhive-network/Rocket.Chat, but we'll need to synchronize changes in iframe events posted by Rocket Chat to Condenser, I suppose.