frontend: log basic request information for each traceback
    
    I always struggle to figure out how some logged traceback was caused
    and how to reproduce it.
    
    This change will probably not be helpful every time but I suspect it
    will make the debugging easier in many cases.
    
    Also, I hope that logging username of a person that caused a traceback
    won't be considered a privacy breach and user tracking. Having a
    contact in case something is notoriously tracebacking for an unknown
    reason would be very valuable and could help us improve the service.