[FEATURE] Add empty Extended Tab to SmartObject TCA

Resolves: #60809
Change-Id: I19c16c3de17063e9624d318a99f777af12012e66
Reviewed-on: http://review.typo3.org/32017
Reviewed-by: Tim Lochmüller <tim@fruit-lab.de>
Tested-by: Tim Lochmüller <tim@fruit-lab.de>