[FEATURE] Become spacious: increase spaces

Backend had been dense for a long time. With larger screens come
more opportunities. Increases vertical and horizontal spaces.

On our way to a backend with less clutter and more space this
is the initial spark.

This patch follows the 12px backend grid raster.

Change-Id: I350a772ee2a52b8b5aed18dbdd44f340b9c17950
Resolves: #48376
Releases: 6.2
Reviewed-on: https://review.typo3.org/20894
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn