Show conference date when conference is scheduled in the future

Test Plan:
  1.  Create a webex conference for a future date
  2.  Verify that the date shows up in the new conferences table

Change-Id: I6592c856c8ed0a3c7264d76f7fd4a4446ef790a2
closes: PS-1102
Reviewed-on: https://gerrit.instructure.com/31884
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Brandon Broschinsky <brandonbr@instructure.com>
Product-Review: Adam Phillipps <adam@instructure.com>
QA-Review: Adam Phillipps <adam@instructure.com>