Launch the experiment.

def launch():
    """Launch the experiment."""
    exp = experiment(db.init_db(drop_all=False))
    exp.log("Launching experiment...", "-----")
    init_db()
    exp.recruiter().open_recruitment(n=exp.initial_recruitment_size)
    session_psiturk.commit()
    session.commit()

    return success_response(request_type="launch")