Timezone of CKAN timestamps should be configurable

[rgrp]

Revisions are timestamped using the server's clock, which may not relate to the expected timezone for the site. e.g. the Norway site has a server on GMT. No timezone info is displayed either.

Would like to set timezone for a CKAN instance to use in rendering revision timestamps. For example, use CET or EST timezone.

[dread]

CKAN timestamps should not be in a timezone, since when the clock goes back, it could cause problems for vdm.

But there may be cases when CKAN is running on a machine that needs the clock set for a particular country (say for a front-end running on the same machine), and so vdm should be changed to create timestamps using UTC specifically (rather than add a timezone, since a mixture of timezones won't sort). And when we display it (or reply to a request) we convert it to the local timezone, as suggested in the description.