Unarmed attacks

* Restores unarmed damage to original values.
* Fixes #7213 (although really using ```attack_damage = min(1,attack_damage - damage)``` in ```apply_effects()``` is a terrible hack and should be cleaned up. I'm not really able to rewrite it just yet).
* Unathi no longer use the xeno bite (I'm not sure why they were using that to begin with).
* Unarmed attack messages no longer assume every attack verb ends with -ed.
* Adjusted some unarmed attack messages to sound less strange to my ears. Let me know if there's an issue.