Ending data stream to user

[shahbuland]

• Need to add ability to remove users with the API

• Add something to API so that when pipeline is exhausted, it automatically removes all users

• Need to update user view once they've been removed
  -> In the simplest case, we add a "Exit" flag to task, that the manager can add to a task
  -> Generate a task with no data and an exit flag, client sees this and switches to a "Thanks for helping!" screen of some sorts

• In some cases, the client might have some data being shown to them, but they've already been removed.
  -> This will require them to submit something
  -> Posting submission will result in error, need the client manager to take submission, dump it, then give back the exit flag