Semantic fix.
Added synchronization, added disabled invalid behavior hooks to
SpacePartitioningGrid for tracking multiple adds of Player to SPG,
resulting in 2x play behavior.
Added time consumption tracking to pinpoint origin of randomly sluggish
performance.
Added bug-catching hooks, window-closing hooks, fixed potential shutdown
crashes.
Added checks for presence of PositionChangeListner before adding in
WorldObject.
More redundant add debug hooks in SpacePartitioningGrid.
Added synchronized wrapping to WorldObject.positionListeners.
Deeper debug feedback for tracking render lag bug.