Add two constant varibles in rules expression

Add two variables:
- UtcTime
The number of seconds that have elapsed since January 1, 1970 (midnight UTC/GMT)
- LocalTime
Seconds passed after Jan 1, 1970 midnight base on current timezone and daylight saving setting.

sonoff/support_rtc.ino

@@ -331,6 +331,11 @@ uint32_t LocalTime(void)
   return local_time;
 }
 
+uint32_t UtcTime(void)
+{
+  return utc_time;
+}
+
 uint32_t Midnight(void)
 {
   return midnight;

sonoff/xdrv_10_rules.ino

@@ -651,6 +651,10 @@ bool findNextVariableValue(char * &pVarname, double &value)
     value = GetMinutesPastMidnight();
   } else if (sVarName.equals(F("UPTIME"))) {
     value = GetMinutesUptime();
+  } else if (sVarName.equals(F("UTCTIME"))) {
+    value = UtcTime();
+  } else if (sVarName.equals(F("LOCALTIME"))) {
+    value = LocalTime();
 #if defined(USE_TIMERS) && defined(USE_SUNRISE)
   } else if (sVarName.equals(F("SUNRISE"))) {
     value = GetSunMinutes(0);