This class is capable of quering a list of people from authors of given posts that are non-contacts of a given
user.

This class implements methods that allow to query relayables (comments, likes, participations,
poll_participations) of other people for posts of the given person.

This class allows to query posts where a person made any activity (submitted comments,
likes, participations or poll participations).

This commit refactors account deletion spec by moving data creation to a helper
object DataGenerator.

Add pod name to FROM: header for no sender case

This improves the main stream when you have less or inactive contacts
and ignored an active person that posts many posts with tags. When the
person is only removed after collecting all post ids, you don't see
posts with tags from other people.

this will help big profiles, and the informations are public anyway, so no
need to encrypt them.

fixes #3164

Related to diaspora/diaspora_federation#35

This was used for the old post fetching

Related to diaspora/diaspora_federation#31

Related to diaspora/diaspora_federation#30

Related to diaspora/diaspora_federation#27

Related to diaspora/diaspora_federation#32

Related to #36

Related to diaspora/diaspora_federation#39

fixes #7195

closes #7455

Fixes #7421

closes #7447

Fixes #7363

closes #7452

Breaking a public key of a person can be used to "block" receiving posts
from this person on the pod. So we should handle that case better and
not just trigger many retries for something that will fail again.

closes #7448

Fixes #7249

closes #7420

Fixes #7438. The regression has possibly been introduced by #7207.

closes #7441

Fixes #4991