First set of bug fixes with the actual device

Some small corrections, now that I can test with the actual power
supplies. At this stage, communication is ok, and the server seems to run just
fine. There are still issues related to the client... most notably the
settings are wrong. Also, device display has to be improved (all hidden
now).
Address some of the problems spotted with the dev

These are not really bugs (except for settings, still pending) but non
practical issues, like the impossibility to know what is going on via
the display and the impossibility to get the error messages from the
hardware.

Also introduced the error logging to file in the client, as the console
is not available in that case.