Resolve "Ensure guest can join earlier, if room becomes active"

What does this MR do?

This MR fixes two issues at once: The issue that guests couldn't join earlier if their patient was already in the room (the nurses being ahead of schedule), and old claimed slots still popped up as orange popups.

Closes #262 (closed)

Closes #250 (closed)

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.
• I have updated the changelog accordingly.