Improve error handling in room history components

[SamuelWei]

Is your feature request related to a problem? Please describe.
Errors that occur when loading the Room Statistics and Room Attendance dialogs are handled with a simple error message.

Describe the solution you'd like
Add a reload button to try again.

If you get the error that room stats is not available, reload the list of all room history meetings to hide the button.

The error handling for room attendance in the backend also needs some improvement, as the error message is misleading.