* common/PropertyManager.cpp: When the PropertyManager is deleted,
set the instance variable to 0.
* server/EntityFactory.cpp, server/EntityFactory.h: Add a destructor
so the property manager can be deleted at shutdown.
* common/PropertyFactory.cpp, common/PropertyFactory.h,
common/PropertyFactory_impl.h, common/PropertyManager.cpp,
common/PropertyManager.h: Add new classes to automate the
creation of property objects for known property types.
* server/CorePropertyManager.cpp, server/CorePropertyManager.h:
Manager object that will coordinate creating properties
when they are added to entities.