Display percentage completion on todos on notes and notebooks

[laurent22]

If a note contains one or more checklist, it should display, in the note list, the percentage completion of these todos.

For example using such an icon:

Same in notebooks, but instead if should show the number of unchecked "to-do" notes. I don't think an icon makes sense in this case - tbd what we display exactly so that's it not confused with the "total note" counter.

If there's no checklist or no to-dos, we don't display anything.

There should be an option to toggle this on or off (default: on).