Same goes for Metadata.

This fixes a regression that was introduced in !551.

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.

Fixes #979

Also removed "personal blog" wording that doesn't apply to RSS blogs.