closets can no longer contain a near infinite amount of mobs.

Closets and its children can no longer contain a near infinite amount of mobs. Fixes #5142 .

* Adding a mob_size var to mob/living to distinguish small, human-sized and large mobs .
 All closets can still contain the same amount of small sized mobs as before(mouse, parrot,pAI, viscerator, lizard, chick, maintenance drones, puppies, kittens).
They can no longer contain large mobs (alien emperess, blobbernaut, juggernaut, hostile tree, goliath).
They can contain a few human sized mobs (2 for bodybags, 3 for closets and other children (numbers can be changed)).

* fixing a very old typo in bodybag.dm

* Adding Bluespace body bag design to R&D. It can hold up to 15 human-sized or large mobs.