client: improve systemconfiguration classbreaks * Use even more width for a single classbreak field so that in case of invalid negative numbers with three digits after the decimal point (e.g. `-0.051`), we can still half the of the right most digit to understand the reason for the problem. * Improve warning message, to leave of the `Please check` part. It is less significant and obvious to the user, because the values have to be checked and corrected before the code allows sending of the new config.

teichmann@intevation.de = sascha.teichmann@intevation.de
bernhard.reiter@intevation.de = bernhard@intevation.de