[TASK] EXT: t3skin - extract table styling

In order to be able to introduce common table css definition,
CSS must be concentrated in a common file "main_table.css".

Change-Id: I3b051577bd0549be074347ce20a41cbeeb3b4b8f
Resolves: #48786
Releases: 6.2
Reviewed-on: https://review.typo3.org/21197
Reviewed-by: Susanne Moog
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Markus Klein
Tested-by: Markus Klein