LP#1697954: Provide client-side sorting for grids that can use it

LP#1697954: Provide client-side sorting for grids that can use it

There are several grids (items out, checkin, checkout, item status, etc) that
could benefit from the ability to sort their items, but either the data
provider uses a complex data structure or an API call that doesn't offer
sorting, or the item list is populated by user input rather than a call to the
server.  In those cases, sorting is not available.  However, if we know that
all the data in the grid is in client memory, it would be reasonable to offer
a client-side sort option.

This commit does that by teaching the grid to accept a "clientsort" feature
and teaching arrayNotifier how to sort the items currently stored.  The sort
works over any mix of IDL objects, hashes, and flattened fields, supports
multisort, and pushes "nulls" to the end of the list.

Signed-off-by: Mike Rylander <mrylander@gmail.com>