Needed for diaspora/diaspora_federation#64

I got feedback from many users, that they don't understand how the "my
activity" stream is sorted, because they have posts on the top, but
don't see why. The user doesn't see if a like was added, and it is also
not imported for the user to see the post again then. And we have
notifications if someone likes a users own posts, so no need to move it on
top of the "my activity" stream here too.

closes #7030

send retraction for relayable to target author if retracted by parent author

also refactored relayable specs to use `let`

* Contact: auto-follow-back
* Shareable: create share visibilities

since it is considered redundant

Fix a security issue that author_signature is not checked on the to-downstream receive of a federated relayable entity, allowing to forge relayables if you are an owner of the pod where a parent object is stored.

closes #6539

closes #6041

* Extract post fetching logic from Reshare into
  its own module
* raise proper error message when fetching fails
* raise proper error message when parent is still missing

We can't skip fetch failures or missing parents and
still need to retry them in case we're sent the parent
later on

we find a better way to reimpliment it in a  more sane way

This reverts commit 655558cb.

Revert "MS DG; for real this time?"

This reverts commit f85a047f.

Revert "MS DG; actually fix the bug"

This reverts commit cde12ec2.

Revert "fix small commenting email bug #oops"

This reverts commit a552fc80.

Revert "dont ban diasporahq  stuff"

This reverts commit 2c12b94e.

Revert "Merge branch 'participants'"

This reverts commit 74178018, reversing
changes made to abd211ba.

add tests for object_should_be_processed_as_public? and delegegated public to the parent of relayable objects

dispatcher