Fix time representation

[lonemadmax]

• There's no need to visit all layers, just the timezone ones.
• Timezones are far from rectangular, testing against their bounds gives wrong results in far too many cases.
• The value in time_zone property is a fixed offset, not taking into account DST changes, so can't be used directly.
• You can now add a timezone property to users to override detection by coordinates (the timezones plugin has stale data, some timezones have changed).
• Changed output format to use client's locale, instead of Swedish.