Sound Additions + Tweaks

Changes listed below:
* Makes Death Sounds mutable on their own audio channel.
* Makes Ear Ringing use the HUD Channel for sounds

Additions:
* [Adds On Fire effect](https://streamable.com/c1fxeo)
* Adds Stunned effect(https://streamable.com/v2if0s)
* [Adds SMES humming based on power usage in/out. Affected by walls, will only play if in LOS and visible.](https://streamable.com/z41x90)
* [Adds Atmos Alerts making a noise on the monitor](https://streamable.com/uhegq6)
* [Tcomms + PDA servers hum when powered and active, also respects walls/LOS](https://streamable.com/vb08x1)
* [Fridges hum quietly while powered](https://streamable.com/c3zsz7)
* [Point Defense turrets now make a sound audible from inside the station when firing, to add more spice to meteor waves.](https://streamable.com/bf8mwl)
* Shield Generators now hum when active.

code/modules/shieldgen/shield_gen.dm

@@ -25,6 +25,7 @@
 	use_power = USE_POWER_OFF	//doesn't use APC power
 	interact_offline = TRUE // don't check stat & NOPOWER|BROKEN for our UI. We check BROKEN ourselves.
 	var/id //for button usage
+	var/datum/looping_sound/shield_generator/shield_hum
 
 /obj/machinery/shield_gen/advanced
 	name = "advanced bubble shield generator"
@@ -41,10 +42,12 @@
 			if(get_dir(cap, src) == cap.dir)
 				capacitors |= cap
 				cap.owned_gen = src
+	shield_hum = new(list(src), FALSE)
 	return ..()
 
 /obj/machinery/shield_gen/Destroy()
 	QDEL_LIST_NULL(field)
+	QDEL_NULL(shield_hum)
 	return ..()
 
 /obj/machinery/shield_gen/emag_act(var/remaining_charges, var/mob/user)
@@ -245,6 +248,7 @@
 			to_chat(M, "\icon[src][bicon(src)] You hear heavy droning start up.")
 		for(var/obj/effect/energy_field/E in field) // Update the icons here to ensure all the shields have been made already.
 			E.update_icon()
+		shield_hum.start()
 	else
 		for(var/obj/effect/energy_field/D in field)
 			field.Remove(D)
@@ -253,11 +257,13 @@
 
 		for(var/mob/M in view(5,src))
 			to_chat(M, "\icon[src][bicon(src)] You hear heavy droning fade out.")
+		shield_hum.stop()
 
 /obj/machinery/shield_gen/update_icon()
 	if(stat & BROKEN)
 		icon_state = "broke"
 		set_light(0)
+		shield_hum.stop()
 	else
 		if (src.active)
 			icon_state = "generator1"