Bug 13037 - Staff client cart should exclude articles when sorting by title

Bug 13037 - Staff client cart should exclude articles when sorting by title

This patch modifies the configuration of the staff client cart table
sorting to enable title sorting to ignore articles. Other column sorting
configuration settings are revised to use table header classes instead
of indexes.

To test, add multiple titles to the staff client cart, choosing several
titles which begin with articles ("a," "an," or "the" in English). View
the cart and test sorting of all columns. Sorting by title should sort
correctly while ignoring articles. Other columns should sort correctly
too.

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Passes tests and QA script, works as described.

Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>