check unread conversation count periodically

fixes CNVS-10558

test plan:
  * open Canvas
  * send yourself a new conversation from another user
  * wait 30 seconds
  * verify that your unread conversation count is updated

Change-Id: I4e9bb2e06bbc862842fbf18e0d77f03afee1bd81
Reviewed-on: https://gerrit.instructure.com/36711
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Joel Hough <joel@instructure.com>
QA-Review: Steven Shepherd <sshepherd@instructure.com>
Product-Review: Braden Anderson <braden@instructure.com>