[TASK] Add cursor:pointer to inline header

the header + icon of a IRRE header should have a cursor:pointer as this is
the area which opens the related record

Change-Id: I71b91f049bf912661d6b6a1e38cb56ba0a9fea1e
Resolves: #44808
Releases: 6.1,6.0
Reviewed-on: https://review.typo3.org/17704
Reviewed-by: Wouter Wolters
Reviewed-by: Ingo Renner
Tested-by: Ingo Renner