Fix horizontal table scrolling within split view

Work packages table with a large number of columns was not scrollable
due to the use of `display: table`/`display: table-cell` on parent
divs with the wrong (default) value set for `table-layout` property.

See: https://developer.mozilla.org/en-US/docs/Web/CSS/table-layout#Values

https://www.openproject.org/work_packages/8234