Bucket users for the Task Recs experiment v1

* If the user is logged in and recently signed up, then they are entered
  into the experiment
* Assign the user to one of the following buckets based on their ID:
    * control
    * post-edit
    * flyout
    * both

Change-Id: I1604b364dade6027c28b92d6711a5182bba3e2ef
Merge "Bucket users for the Task Recs experiment v1"