unify periodic timers

src/PeriodicTask.cpp

@@ -0,0 +1,19 @@
+#include "PeriodicTask.h"
+#include "Periodic.h"
+
+PeriodicTask::PeriodicTask(uint32_t initialPeriod) : period(initialPeriod)
+{
+}
+
+/// call this from loop
+void PeriodicTask::loop()
+{
+    uint32_t now = millis();
+    if (period && (now - lastMsec) >= period)
+    {
+        lastMsec = now;
+        period = doTask();
+    }
+}
+
+  uint32_t Periodic::doTask() { return callback(); }