Add caching to air alarms, apcs and power monitoring computers

code/datums/cache/powermonitor.dm

@@ -0,0 +1,24 @@
+var/global/datum/repository/powermonitor/powermonitor_repository = new()
+
+/datum/repository/powermonitor/proc/powermonitor_data(var/refresh = 0)
+	var/pMonData[0]
+	
+	var/datum/cache_entry/cache_entry = cache_data
+	if(!cache_entry)
+		cache_entry = new/datum/cache_entry
+		cache_data = cache_entry
+
+	if(!refresh)
+		return cache_entry.data
+		
+	for(var/obj/machinery/computer/monitor/pMon in world)
+		if( !(pMon.stat & (NOPOWER|BROKEN)) )
+			pMonData[++pMonData.len] = list ("Name" = pMon.name, "ref" = "\ref[pMon]")
+
+	cache_entry.timestamp = world.time //+ 30 SECONDS
+	cache_entry.data = pMonData				
+	return pMonData
+	
+/datum/repository/powermonitor/proc/update_cache()
+	return powermonitor_data(1)
+