allow to add genre or topic to multiple items

[maxlath]

It's currently possible to select multiple inventory items to change their visibility or transaction in bulk. In the same way, and possibly in a nearby GUI, it could be possible to add a genre or subject to the works entities associated with several inventory items at once (letting authors aside to avoid confusion between work primary authors and edition contributors?).

It would be nice to settle the genre modelization question before opening this possibility though, see https://github.com/inventaire/inventaire/issues/316