Privileged Entity update + Pubsub Account Management partial implementation + Public Pubsub Subscription /!\ pgsql schema needs to be updated /!\ /!\ server conf needs to be updated for privileged entity: only the new `urn:xmpp:privilege:2` namespace is handled now /!\ Privileged entity has been updated to hanlde the new namespace and IQ permission. Roster pushes are not managed yet. XEP-0376 (Pubsub Account Management) is partially implemented. The XEP is not fully specified at the moment, and my messages on standard@ haven't seen any reply. Thus for now only "Subscribing", "Unsubscribing" and "Listing Subscriptions" is implemented, "Auto Subscriptions" and "Filtering" is not. Public Pubsub Subscription (https://xmpp.org/extensions/inbox/pubsub-public-subscriptions.html) is implemented; the XEP has been accepted by council but is not yet published. It will be updated to use subscription options instead of the <public> element actually specified, I'm waiting for publication to update the XEP. unsubscribe has been updated to return the `<subscription>` element as expected by XEP-0060 (sat_tmp needs to be updated). database schema has been updated to add columns necessary to keep track of subscriptions to external nodes and to mark subscriptions as public.