Bug 26782: Add new class for indicating default sort without sortability

Bug 26782: Add new class for indicating default sort without sortability

This patch adds to the globally-included CSS a class which can be added
to tables when they are configured using DataTables options that set a
default sort but don't allow the user to reorder columns.

The new class shows a grey rather than blue sorting indicator and sets
the cursort to the default pointer rather than the link "hand."

To test, apply the patch and rebuild the staff client CSS
(https://wiki.koha-community.org/wiki/Working_with_SCSS_in_the_OPAC_and_staff_client).

Go to Administration -> Circulation and fine rules

In the table of circulation rules, confirm that the first two columns,
"Patron category" and "Item type" have a grey sorting icon in the
header cell indicating ascencing sort. Hovering the cursor over these
cells should show a default arrow cursor rather than the link cursor.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>