As any world can contain multiple domains, we let the domain handle the
sights calculations.
This is a change from how this previously was done, as previously
sight checks were only done for the top level World entity. This has
changes however, so that sights checks now are done for all entities.
When determining whether an entity can be seen, the system first checks
the size of the entity against the distance from the observer. If this
check fails, the system makes exceptions if the entity in case is
outfitted or wielded.
