Date/Time options should ask for DST "zone"

[orangenormal]

It should be possible to select from possible DST zones so WordPress can account for Daylight Saving Time in those regions. Only storing an offset from UTC doesn't account for Daylight Saving Time.

Here are all the possible DST regions:

​http://webexhibits.org/daylightsaving/g.html. DST could be accounted for by doing a simple test to see if UTC+offset is within these dates (i.e. the time should be calculated as UTC+offset+DSToffset, where DSToffset is 1 only if within the limits from the above website)