Generic ventcrawling + Bugfixes

This commit makes the ventcrawling system operate independant of
ventcrawling verbs. Every type of /mob/living now has a ventcrawling
variable, which allows them to interact with the ventcrawling system if
set to 1 or 2. The AltClickOn() defines for each ventcrawling mob have
been removed, and replaced with a single AltClick() define on ventcrawl
machinery.

code/ATMOSPHERICS/atmospherics.dm

@@ -184,5 +184,11 @@ obj/machinery/atmospherics/proc/check_connect_types_construction(obj/machinery/a
 	spawn(1)
 		user.canmove = 1
 
+/obj/machinery/atmospherics/AltClick(var/mob/living/L)
+	if(is_type_in_list(src, ventcrawl_machinery))
+		L.handle_ventcrawl(src)
+		return
+	..()
+
 /obj/machinery/atmospherics/proc/can_crawl_through()
 	return 1