test that AP direct messages are converted to XMPP `<message>` stanzas instead of pubsub
items.
test that XMPP `<message>` stanzas are converted to AP direct messages (i.e. items
addressed solely to the recipient, without *followers* or *public* collections).
rel 366
are covered:
- AP actor handle to XMPP JID/pubsub node
- XMPP JID/pubsub node to AP actor handle
- AP request to JID/pubsub node (AP collection to items/RSM metadata conversion)
- pubsub request to AP actor (pubsub request with RSM to AP collection/pagination requests
conversion)
ticket 363