Added part system back-end

Sign on exterior is now lit by default matching interior doors (will add
st john sticker soon). Interior doors are now serverside and have proper
collision (uses new part system). Enabled popular double trace feature
from legacy. Added ShouldThink hook for various things to try and
improve performance for people not in the interior. Added parts system
which is a vast improvement on the old version from legacy and includes
such things as dark magic, automatic optimisations and a plugin style
layout. A test button has been included somewhere on the console.
Removed the 'secret wall'.