set css class "thead-*" at CE table

[zonky2]

set css class "thead-*" at CE table

if "thead-*" in CSS-Class and table head exist, should move the class to the thead tag

see https://getbootstrap.com/docs/4.3/content/tables/#table-head-options

[dmolineus]

The table classes are rewritten in the layout component (i'm not happy about the location but that's another story). So I moved the issue