Fix ElevatorAttendant so it detects button-press (when it goes down)

Detecting the first time the button goes down permits us to do the expensive one-time kinds of things (like logging, initializing from SmartDashboard. If we can log a message on the first time a button is pressed, we avoid flooding the logs with too much information. You'll need to read about getting buttonDown events from the controllers. I don't think it is too hard.

Start by locating ElevatorAttendant and reading how it currently handles controller button state. Review the controller documentation for buttonDown events, then verify that the first downward transition enables one-time actions such as logging or SmartDashboard initialization without repeated messages.

Written by the indexing model from the issue text.