Resolve "Have an "upcoming visit" popup on the guest page"

What does this MR do?

The server gets pinged every 1 minute to see if there is an upcoming timeslot for the user within the next 5 minutes. If so a card will be displayed with this information on it and a link to the room.

Screenshots

before

after

Does this MR meet the acceptance criteria?

• I have added tests to validate the new functionality.
• I have updated the documentation accordingly.
• I have added translations for all new client-side text. closes #89 (closed)