DEV: patchbot: add an "O" filter to hide original lines without new notes

DEV: patchbot: add an "O" filter to hide original lines without new notes

Now that we can save notes, it appears that it becomes convenient to
leave new backport notes there, e.g. flag the already backported patch
as "wait" and add a note "left in 3.2 for now, sensitive backport". But
rediscovering these notes later happens to be difficult.

This patch adds a new checkbox with "O" for "original notes", which
is checked by default, and which when unchecked allows to only list
lines with edited notes.

An initial test was made to also consider a changed state in this reduced
listing but too many are changed (~10%) and they add pollution for no
reason (many Y<->N). Let's just keep lines with extra notes.