cubicweb #1164908 Selection mecanism when creating a relation is broken [resolved]

When one wants to create a relation using the generic mecanism (modify an entity, select "add a relation"), she cannot select the target entity (the link does nothing).

done in3.9.1
load left0.000
closed by#348cf2a14cc1 [forms] we need a wrapping list to avoid bug caused by flatening done by $.map. Closes #1164908