[MWR] Mutant gear

Includes XL versions of gas mask & rebreather, stipulates that earplugs can fit no matter the head and makes them Oversize just to be sure, and two varieties of mutant-friendly jumpsuit.

Tentacle-stockings & hoof-warmers too, though those'll get changed once we refactor mutations.

Answers #4971.  Issue should remain open, please, as we/I should get mutation-specific tailoring coded up.

Merge when ready, please.