Add timezone to message feed header

[cc-a]

Kafka messages are stored in the database with UTC timestamps. When rendered in the message feed these are converted into the localtime based on the django TIME_ZONE setting. At the moment there is no indication of what timezone is being used. We should add this info into the header of the message feed - preferably the geographic timezone as well as the UTC offset (e.g. "London/Europe (UTC+1)".