Don't cache signature and anonymous individuals everywhere

Create parallel hierarchies for OWLObjectImpls with and without signature and anonymous individual caching. 

This can save 8 bytes per object (which includes Literals, Properties, etc.) 

Using OpenCyc.owl as benchmark, 

Before: 621,444,560 total ; Internals 458,017,704
After:  587,437,336 (94.5%) ; Internals 429,956,616 (93%)