Add back boots and gauntlets for invaders

[pjf]

From #15 , of which this is essentially a more detailed sub-ticket:

• I know that gloves and boots were removed from all invaders to reduce clutter, but this also has the side-effect of making invaders significantly easier against fledgling militia. Strikes to hands and feet aren't all that uncommon, and they're very effective at disabling targets, especially with edged weapons. I keep having elves and drow arrive with their mithril and bloodsteel armors, but because they're not fully covered, they're relatively easy to kill.
• I have to double-check, but I seem to recall of all the elven ambushes and sieges I've encountered, none of them have been wearing pants. I know they're elves, and so that's thematic, but it means elves are now an easy source of mithril, rather than a serious threat.

This could be made a configurable option, if folks really don't want invaders with more armour.