Regression: sorting the document listing in unordered folders is broken

Clicking on a header to sort the column works only the first time and doesn't update the header visually. The column data is updated correctly, but likewise only for the first click.

This is due to the AjaxFallbackHeadersToolbar calling newSortableHeader() after every click on the toolbar since Wicket6. This call creates a new object ListTableHeader which sets an initial ascending sort order on the first name column it finds and hence fixes the sorting to name-ascending for all non-orderable folders.

Reproduction path:

• Start up the test-suite
• Navigate to folder demosite/common
• Click on a table header to change the sorting

Expected: table is sorted by the column we clicked on, where direction changes state in the following order: natural-order, ascending, descending. This state is also reflected by the column header.
Actual: Table is sorted ascending by name, no matter what.