Smart outlet heartbeat fix

-Readded heartbeat calls that were accidentally removed.

devicetypes/smartthings/smartpower-outlet.src/smartpower-outlet.groovy

@@ -69,6 +69,9 @@ metadata {
 def parse(String description) {
 	log.debug "description is $description"
 
+	// save heartbeat (i.e. last time we got a message from device)
+	state.heartbeat = Calendar.getInstance().getTimeInMillis()
+
 	def finalResult = zigbee.getKnownDescription(description)
 
 	//TODO: Remove this after getKnownDescription can parse it automatically
@@ -109,6 +112,7 @@ def on() {
 }
 
 def refresh() {
+	sendEvent(name: "heartbeat", value: "alive", displayed:false)
 	zigbee.onOffRefresh() + zigbee.refreshData("0x0B04", "0x050B")
 }