Broadens hat encumbrance

This adds encumbrance and the VARSIZE tag to most hats.  It's intended
to discourage wearing multiple hats & helmets over hats.

(It's possible to wear one hat over another IRL--I've done it--but only
if the first fits you well and the second is a bit looser.  Bulky
headgear should prevent other stuff on top of it.  (Top hat, I'm looking
at you.)
Merge pull request #7778 from KA101/HatFitting

Broadens hat encumbrance