Create a UserRegistrar system (like the existing RobotRegistrar) to provide a centralised way to listen for user creation etc.
Will want to merge the code from RobotRegistrar (where similar), and combine the user account creation methods from RobotAgentUtil and UserRegistrationServlet.
Change WelcomeBot to act as a listener instead of manually calling it where needed.
Create tests (mostly a case of renaming UserRegistrationServletTest)
Minor