Viz

this is the revived and reimplementation of DFM tracing facilities via a structured output, using the serialization library.

planned is to implement a frontend in javascript and get it used.

these changes
 * survive a 3stage bootstrap
 * increment compile time and space usage (each flow node has an <integer> associated)
 * once tracing is enabled (via interactive command-line property ``set visualization <host>:<port>``), messages are sent to the specified host and port (default: 1234)

feedback is very welcome. I'm also happy to get this merged and continue developing based on this changeset.