- Added a file system watcher
- corresponding start command
- corresponding stop command
- reads and displays the trace on change file system events
- try with e.g. an equivalent of the following command:

cp /home/jwintz/Development/elpi/tests/sources/trace_findall.elab.json /tmp/traced.json

- either when the watch is running
- either when the watch has stopped

- Needs visual hints