Xenomorphs fixes and improvements (#3548)

This pr makes xenomorphs less awful via some additions and porting some fixes:
-removes the NO_MINOR_CUT that is not used anywhere and replace with NO_EMBED that stops things from embedding into mobs, like xenomorphs, shadow people and golems
-adds the night vision verbs to xenomorphs
-fixes aliens eggs layers behind under their weeds
-fixes some hud things missing
-makes their limbs unbreakable

This should make them a bit less buggy.

code/game/objects/structures/alien/alien.dm

@@ -2,6 +2,7 @@
 	name = "alien thing"
 	desc = "There's something alien about this."
 	icon = 'icons/mob/alien.dmi'
+	layer = 4
 	var/health = 50
 
 /obj/structure/alien/proc/healthcheck()

code/game/objects/structures/alien/egg.dm

@@ -83,6 +83,7 @@
 	// Create the mob, transfer over key.
 	var/mob/living/carbon/alien/larva/larva = new(get_turf(src))
 	larva.ckey = user.ckey
+	xenomorphs.add_antagonist(larva.mind, 1)
 	spawn(-1)
 		if(user) qdel(user) // Remove the keyless ghost if it exists.