[TASK] Extension manager fixed DocHeader

Fixes the docheader rows in their top position by using the
standard css id "typo3-inner-docbody".

Also includes the new 6.0 docheader html tags.

Change-Id: Ifce74f41d1f882a5cb7095bc3546a0685935b688
Resolves: #42455
Releases: 6.0
Reviewed-on: http://review.typo3.org/15991
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn