Add the timezone in date/time meter

... just as done in clock meter.

DateTimeMeter.c

@@ -26,7 +26,7 @@ static void DateTimeMeter_updateValues(Meter* this) {
 
    struct tm result;
    const struct tm* lt = localtime_r(&host->realtime.tv_sec, &result);
-   strftime(this->txtBuffer, sizeof(this->txtBuffer), "%F %H:%M:%S", lt);
+   strftime(this->txtBuffer, sizeof(this->txtBuffer), "%F %H:%M:%S %Z", lt);
 }
 
 const MeterClass DateTimeMeter_class = {