This eliminates the O(N^2) (N = map leaf count) operation of finding
visible lights and will later allow for finer culling of the lights as
they can be tested against the leaf volume (which they currently are
not as this was just getting things going). However, this has severely
hurt ad_tears' performance (I suspect due to the extreme number of
leafs), but the speed seems to be very steady. Hopefully, reconstructing
the vis clusters will help (I imagine it will help in many places, not
just lights).
I don't know why it didn't happen during the demo loop, but going from
the start map to e1m1 caused a segfault due to the efrags for a lava
ball getting double freed (however, I do think it might be because the
ball passed through at least two leafs, while entities in the demos did
not). The double free was because SCR_NewScene (indirectly) freed all
the efrags without removing them from entities, and then the client code
deleting the entities caused the visibility components to get deleted
and thus the efrags freed a second time. Using ECS_RemoveEntities on the
visibility component ensures the entities don't have a visibility
component to remove when they are later deleted.
