cubicweb-conference #978006 add relation is_chair_at and is_reviewer_at [resolved]

to have more precise permissions and more precise information at some places.

prioritynormal
typeenhancement
done in0.7.0
load0.300
load left0.000
closed by#cbf6554dd8f3 [all] add relations is_chair_at and is_reviewer_at (closes #978006)