Split "suppressrevision" into two user rights

In this change, a new passive user right named "viewsuppressed"
which can be used in order to view suppressed page content was added
to MediaWiki core.
Furthermore, this right was also added to the list of available rights,
to qqq.json and to en.json where also the description of the
"suppressrevision" right was adjusted in order to reflect reality.

Bug: 20476
Change-Id: Id1baacb9c782763db5e05ef8b5c1b761997efcc9