also drop xml-code for Shareable

handle photos in StatusMessageCreationService

this creates inconsistent states, if you remove the block in the future

also refactored receive methods

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

all visibilities are already in the conversation, so we can send
all notifications at once.

* conversations
* messages
* photos
* polls
* poll answers
* poll participations

fixes #4697