Rename post-view to single-view

single-view, used to see a specific revision (for diff pages, I think) was
called post-view, which is ambiguous (that's the 'view' name for the new API
post-specific view) and (I think) incorrect, as there was nothing linking to
'post-view'.
Meanwhile also fixed block name for single post view.

Change-Id: I06988bf3dc94830f25e707d5d4d232e1977b51a8
Merge "Rename post-view to single-view" into frontend-rewrite