Remove block physics.
Fix unparameterized types in EntitySpatialTreeIndex.
Fix unparameterized types in BouncyDemo.
Refactoring BouncyDemo.  Currently compiles but does not advance.
Fix: Update EntityTreeNode#nextAutoUpdateTime when an entity is added.
Work on making simulation time not have to be the same as real time for BouncyDemo.  Not quite working yet.