[Ovmsdev] Config framework: race condition fix & storage transaction scheme [PR #1310]

Happy new year everyone :)

I've been working on a somewhat larger rework of the config framework:

https://github.com/openvehicles/Open-Vehicle-Monitoring-System-3/pull/1310

This touches a lot of places and changes an 8 year old foundational framework component, so I'd love to get some audit and test feedback for this before actually including this in the edge build.

Thanks & kind regards, Michael

-- Michael Balzer * Am Rahmen 5 * D-58313 Herdecke Fon 02330 9104094 * Handy 0176 20698926