Makes nursery somewhat usable

This makes nursery children actually retrievable from the facility.

Also corrects some nitpicking like the "$He" typo in the child summary list descriptions, and the universal rules default destination checking on the nannies instead of the children rooms for available slots.

This basically makes InfantState inherit from SlaveState (with a lot of removing defaults) and maskerades as a tankchild in the "can-opening" passage, with a few ifs to avoid tank-specific methods and descriptions.

This does not touch interaction at all, that's still broken AF.

Growing up has been tested using a fast-forward hack I've added in the debug tools, adding a week, month or six months at a time but only running endWeek(), slaveAssignmentReport(), economics() and nextWeek() in a loop. That means events get lost, but I haven't found any nursery-specific ones, so it should still be okay for testing this.

Any child already in the nursery is probably still lost at this stage.