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
Same technique as https://github.com/fortressforever/fortressforever-scripts/pull/1#discussion_r21135812

The `or function() end` is just some redundant safety that basically means 'if security_on is nil, then set security_on_base to a dummy/blank function.' This is done to make sure that `security_on_base()` is always safe to do without having to check its type.