Require grabbers to correctly handle timezones

[perkins1724]

Currently timezones are handled by the augment_timezone post processor. If the source containing augment_timezone goes down but a separate source with grabbers remains then it is possible to get output but with wrong timezones. We should be requiring grabbers to output timezone correct data and honour it through the shepherd program chain and retire augment_timezone.

[thiakil]

All grabbers should probably also move to using DateTime and DateTime::Format modules which are timezone aware as opposed to calculating static offsets or using raw posix functions.

So grabbers which deal with localtime can create the object with timezone set to Australia/X and it should 'just work'