* common/types.h: Add a function pointer type, and related
typedefs for functions which handle an operation.
* rulesets/Entity.cpp, rulesets/Entity.h: Add a map of operation
handlers so that any operation type can be handled by data
defined handlers.
* rulesets/ActivePropertyFactory.cpp, rulesets/ActivePropertyFactory.h,
rulesets/ActivePropertyFactory_impl.h: Add a new type of property
factory, which installs a handler when the property is added to
an entity.
* server/CorePropertyManager.cpp: Test out the new property factory
and handler mechanism with a new property called "attachment".
