[BUGFIX] CE Table does not allow multiple css classes

When using the content element "table", a
field within the flexform shows the possibility
to add an additional css class for the table.
however only one css class can be added.
When adding "myclass1 myclass2" this is not
possible as the evaluation is too strict.

Releases: 6.2
Resolves: #55470
Change-Id: I697184398067add518e750054dd327e741a91de7
Reviewed-on: https://review.typo3.org/27161
Reviewed-by: Benjamin Kott
Tested-by: Benjamin Kott
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters