Give some indication of the time zone of the talk

[envycontent]

We are returning the start and end date and time as ISO 8601 in UTC and also giving a formatted string of the start date and time (only) in the local time zone. The local time zone is the time zone of the location of the talk and is assumed to be GMT/BST . At present we don't expect to have talks in Oxford Talks outside of that time zone, but should we be explicit about the time-zone - some thoughts:

• providing a time zone field in the API
• an additional ISO 8601 with the appropriate offset in the API
• a country field for the location in the UI