UniDataTable does not refresh UI when a column's Sort property changed

[miyconst]

As of right now, UniDataTable does not reflect server side changes to the column.Sort property.

Steps to reproduce:

• Create a page with UniDataTable and at least one column.
• Create a button on the page.
• Let the button clear the sorting of the table column.
• Load the page.
• Sort by the column.
• Click the button.
• Sorting is removed, but column header does not reflect the changes.

protected void Handle(Input.ClearSortingTrigger action)
{
    (this.DataTable as Starcounter.Uniform.ViewModels.UniDataTable).Columns.First().Sort = null;
}

[warpech]

Reopening. The problem was fixed in a clone of this repo, but not here.

@tomalec will you take care of this?

[tomalec]

Extended solution available at https://github.com/Starcounter/uniform/pull/247
BC would have to upgrade to cover all the scenarios.