Use std logging module

This pull-request bases the logging-engine on the standard Python logging module. This leads to the following user-visible changes:

 * Log-level names are all upper-case now
 * for console-output: the human timestamp-format is *always* used
 * for local-log: the human timestamp-format is *always* used
 * for messages send as Broks to the broker: the human timestamp-format is *never* used