[TASK] Tab key for backend layout config

Modify the backend layout TCA so that pressing the tab key
will not jump to the next field but insert a tab in the
config field.

Change-Id: I7e84cc7d47d5fcfba48dae0d67a93575913fc200
Reviewed-on: https://review.typo3.org/31034
Tested-by: Daniel Gorges
Tested-by: Thomas Schlumberger
Reviewed-by: Jo Hasenau
Tested-by: Jo Hasenau