Add a list of time zones in the Add/Edit meeting form

This allows the user to specify the time zone of the new meeting.
Display the new time zone fields in the Add and Edit meeting forms.
Implement logic of the timezones switch in the controller

- Adjust the list of time zone to defaults to the user's specified one (retrieved from FAS)
- Propagate the specified timezone to the backend which deals with it
Define the timezone earlier based on what the user filled on the form
Merge pull request #40 from fedora-infra/tzone_edit

Tzone edit