Hardware: Finish, order and test the "isolated" IO board variants

[kripton]

For cost reasons and since I didn't know for sure if all features I had in mind actually work, I only ordered, soldered and tested the "unisolated" variants of the IO boards.
The "isolated" (= galvanically isolated and better protected against ESD) variants are more or less done but are yet untested. They are more expensive since they require DC/DC-converters with quite some output power and the isolated RS-485-driver ICs are more expensive than the non-isolated ones.