Fix Blog Sharing Sessions
This MR moves responsibility for pre-sharing blogs to the sharing manager to have all the code related to that in one place, so it is easier to maintain and to spot bugs.
This also checks that only blogs without an existing sharing session are shared and initialized again. It extends an existing test to catch the missing check.
This removes some debugging information from the previous commit to not leak private information via the sharing sessions.
Please review carefully as this is a delicate last-minute fix that might very well introduce new issues.
Fixes #979 (closed)
Edited by Torsten Grote