cubicweb-vcreview #2522747 Allows comments on task only [validation pending]

The ability to comment a chunk of a patch being reviewed should be removed. Only tasks should be kept here. Comments are not visible, and very easily lost or just ignored. If one has something to say about a part of a reviewed patch, it means something has to be done by the patch author (whether it be to choose not to reject the comment), thus it is a task.

but people need to be able to discuss a task

done in1.1.0
load left0.000
closed by#ef49cb5a2e7d [schema] force comment to be on a task (Closes #2522747)
patch[schema] force comment to be on a task (Closes #2522747) [applied]