hatch bug

Just had a long chat with Owen about this. The bug was: hatched agents were getting too many of their parents properties (notably, things like objects, which meant several hatched agents would all end up with references to the same object, when you'd expect them instead to have clones).

We decided for now to copy over a much smaller subset of parent properties: only those declared with `breed.owns()` that haven't already been defaulted to a certain value.

I also threw in color, since it was bugging me that hatched children were no longer inheriting parent color after the fix.

This might not be the right solution. Maybe more thinking to do about this. Merging for now though.