Refactor floodlights

- Fixes #9543
- Removes ugly floodlight/proc/updateicon() and replaces it with proper floodlight/update_icon() which is standard on all objects/items. Does the same refactor for power cells and adjusts the proc call in relevant files (hence the amount of 1-line changes in various files)
- Makes floodlights properly use CELLRATE. Their load is 200 watts. Cell adjusted accordingly, it starts with 1k cell, which is enough for ~40 minutes (roughly)
- Floodlights with almost discharged cell (less than 10%) ocassionally "flicker", dimming for few seconds. This serves as indicator that the power cell is running low.
- Floodlight luminosity adjusted. They now shine slightly more, espicially closer to the floodlight.

code/modules/power/cell.dm

@@ -8,7 +8,7 @@
 
 /obj/item/weapon/cell/initialize()
 	..()
-	updateicon()
+	update_icon()
 
 /obj/item/weapon/cell/drain_power(var/drain_check, var/surge, var/power = 0)
 
@@ -22,7 +22,7 @@
 
 	return use(cell_amt) / CELLRATE
 
-/obj/item/weapon/cell/proc/updateicon()
+/obj/item/weapon/cell/update_icon()
 	overlays.Cut()
 
 	if(charge < 0.01)