Display outbox interface

[jum-s]

Having an entity-history-like interface retracing outbox activities of local actors.

Intent:

• make activities more visible to users
• giving a way to check recent activities, to see if an actor is active

All necessary data should already be available on outbox endpoint.

No integration in the current interface is foreseen for the moment, since it may not be necessary (aka other "hidden" mechanisms such as RSS or JSON rendering).