Setting half-hour timezones

[silseva]

Now the timezone can only be set on whole hours, but there are several timezones on the half hour like +9:30 Adelaide, Darwin,... Change the timezone setting code to allow for half-hour zones. Variable state.settings.utc_timezone should store the timezone expressed in halves of hours, i.e. the timezone UTC+1 should lead to have the state.settings.utc_timezone equal to two.