cubicweb-medicalexp #3455812 add a "participates_in" relation [validation pending]

Add a "participates_in" relation between a Center and a Study

prioritynormal
typebug
done in0.7.0
load0.200
load left0.000
closed by#f7db306c5ce4 [schema] Add a "participates_in" relation, closes #3455812
patch[schema] New relation particpates between Center and Study [applied]