[FEATURE] Show contentelement "header" in wizard

It makes sense to show this content element in the
wizard as every other type is shown there too.

Change-Id: I983583b9c2dc519906f881a0a40c4e2af520b0c8
Resolves: #45548
Releases: 6.1
Reviewed-on: https://review.typo3.org/18337
Reviewed-by: Thomas Loeffler
Tested-by: Thomas Loeffler
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers