Activities for entities lists

[jum-s]

Create and publish activities about entities lists updates.

In other words, create activities for elements in a list.

It could be that implementation might end up transforming how activities are created for users actors, which would be based on creating activities on-the-fly/at the moment the outbox request, and not stored at items creation (like today). This would have the advantage of having up-to-date lists of activities (because now, some items updates are not taken into account, missing some activities creation, ie. items that was private become visible)