Fixing save task initialization step.

The line index was not re-initialized leading to second file never being closed.
Hopefully final fix to measure saving.
Adding some log messages to process engines and make news use Signal rather than Event.
Light modifications to check and header editors.
Some fix to monitors.
Small changes to measure_exec pane.
Starting to implement a PairEditor on top of ListEditor for tasks (save, formula, def, pna)
All task use new pair editor (save PNA tasks).
Numerous fixes to monitor UI.
Merge branch 'pair-editor' into plugin-feature
Fix reloading issue in driver_debugger.
Fix kwargs evaluation in driver debugger.