Data request display does not handle time zones properly

[ThrawnCA]

Data requests are displayed with inaccurate "Created" strings, eg "-1 days ago".

This appears to result from a lack of time zone handling. actions.py populates the creation timestamp without specifying a time zone, but when it is rendered, it uses a localisation method (formatters.localised_nice_date) that assumes a lack of time zone data means UTC.

Either the time zone should be specified when first creating the data request, or else the current server time zone (eg from helpers.get_display_timezone()) should be assumed when displaying it. The latter approach would also resolve existing data requests.

This is similar to ckan/ckanext-xloader#102