CFME header logging

I found this branch, so I repolished it and it seems working. It writes what does selenium do in the header line.
It looks like createSpan could take `toWrite` and `logger_span_id` as args, and then live in lib.js. We went through all the trouble to consolidate the js in there, it'd be a shame to go back to burying it in py files.

theConfusion with_identifier_styling IsALittleDistracting.