Better base_shutdown.lua

 * Add built-in support for trigger-based buttons (blue_security_trigger/red_security_trigger)
 * Add built-in support for Lua-defined security shutdown length (SECURITY_LENGTH)
 * Add built-in support for turning on/off lights, brushes, trigger_ff_clips, and trigger_hurts
 * Add some helpful team-oriented trigger definitions in base_teamplay.lua
Does this allow scripts to define their own startup function?