feat: reread config file on each pass of plot loop

[wtfrank]

Allows settings such as number of threads to be tweaked without restarting "plotman plot".

[altendky]

This would at least need to be configurable. I share my configs between multiple machines and use git to transfer between and so various changes could get loaded that do not make sense while I am processing through that. Also, what should happen if the reload fails?

[mk01]

@altendky of course old config should be retained.

            try:
                newcfg = configuration.get_validated_configs(configuration.read_configuration_text(config_path), config_path)
                cfg = newcfg
            except Exception as ex:
                print('... while reloading config: %s' % (str(ex)))