Add blackout button

Add a blackout smart button to work with #6.

- disables headlights and taillights
- disables specified extras (already implemented)
- disables real-brake-lights script

Method for disabling real brake lights script:
- add events to the script to disable and enable the effect
- call even from ULC
- possibly make it re-enable when the vehicle starts moving?
- add a command and keybinding in real-brake-lights to control this manually (this one has nothing to do with ULC) (well, maybe if it's re-enabled in the other script ULC needs to know about that)

Start by reading the ULC entry points and the real-brake-lights script, then review issue #6 for the existing blackout behavior. Trace how ULC handles smart buttons, events, commands, and keybindings. Done means the blackout button controls headlights, taillights, specified extras, and real-brake-lights, with the intended moving-vehicle behavior agreed and tested.

Written by the indexing model from the issue text.