SOLN 2042: Expect date value to contains timezone info

Previously: date value was obtained from survey.launch_on or survey.close_on
- It only contained the date info with no associated timezone.
- This caused problems when the client assumes value is in UTC (although it may already be in the local timezone), and then converts it from UTC to the local timezone
Update: Expect value to be obtained from survey.launch_on_datetime or survey.close_on_datetime.
- It will then have timezone information associated with it, which can be correctly passed to the client.

For example: Before: Using launch_on Database launch_at: 2019-02-05 18:00:00 (in UTC) get_date_value(:launch_on):

survey.launch_at = Tue, 05 Feb 2019 10:00:00 PST -08:00 (ActiveSupport::TimeWithZone)
survey.launch_at.iso8601 = "2019-02-05T10:00:00-08:00" (String)
value = survey.launch_on = survey.launch_at&.to_date = Tue, 05 Feb 2019 (Date, in the local timezone)
value.to_time = 2019-02-05 00:00:00 -0800 (Time)
value.to_time.iso8601 = "2019-02-05T00:00:00-08:00" (String)
value.to_date = value =Tue, 05 Feb 2019 (Date, in the local timezone)
value.to_date.iso8601 is "2019-02-05" (String)

After: Using launch_on_datetime get_date_value(:launch_on_datetime):

value = survey.launch_on_datetime = survey.launch_at&.to_time = 2019-02-05 10:00:00 -0800 (Time)
value.iso8601 = "2019-02-05T10:00:00-08:00" (String)

techvalidate / pano