Improve NTP handling (#1676)

* fix special case where number is named "default" (keep all topics in top level instead of in a sub-group)

* re-implemented SNTP usage, added way to disable NTP client, added timezone table

* minor fixes

Co-authored-by: CaCO3 <caco@ruinelli.ch>

code/components/jomjol_fileserver_ota/server_ota.h

@@ -15,6 +15,5 @@ void CheckOTAUpdate();
 void doReboot();
 void hard_restart();
 void CheckUpdate();
-static bool ota_update_task(std::string fn);
 
 #endif //SERVEROTA_H