cubicweb-vcreview #1655113 Make it possible to comment the header of a patch [resolved]

For now, a patch is divided in diff shunks which is the unit on wich a comment (or a task) can be attached to. It should be possible to attach a comment on the header of the diff (to comment the comment of the commit).

done in0.5.0
load left0.000
closed by#f8c711cd825d allow to add comment and task on commit message (closes #1655113)