Initialize() method, called (for GameObject bean properties)
after instantiating the property, and cloning it if it's a
MutableProperty, but before it's added to the destination
PropertyList.
Instantiates an archetype the same way
instantiate(arch) does, except that it uses
the passed classname, instead of the classname specified
in the archetype.
Takes an Archetype that we parsed, turns it into a GameObject
inheriting from the archetype, and copies certain properties
from the Archetype to the object.