Use topicLink() to create notificaiton main URL

* workflowLink() is the old format, it would fail for old notificaiton
  because old notificaitons have board title as title and it's not
  a topic namespace

* old notifications had board title as title, and that's used to built
  the postLink, we could force a title lookup on workflowid, but that's
  extra data processing.  We agreed that this is fine for old notifications

Change-Id: I549b413ccac9a46798257bb4d9f9f38d0a49ac75
Merge "Use topicLink() to create notificaiton main URL"