table sorting should have directional indicator

[Thai Tran]

Currently, it is not possible to know which column determines the sort order for the table. It will be helpful to have an directional indicator that let users know which column is being sorted AND in the direction of the sort.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/75553

[Openstack Gerrit (openstack-gerrit)]

Reviewed: https://review.openstack.org/75553
Committed: https://git.openstack.org/cgit/openstack/horizon/commit/?id=7605a3692cd004ae36a3dc485093fb8bb754a873
Submitter: Jenkins
Branch: master

commit 7605a3692cd004ae36a3dc485093fb8bb754a873
Author: Thai Tran <email address hidden>
Date: Fri Feb 21 18:34:37 2014 -0800

    Add sort indicator to table headers

    Currently, it is not possible to know which column determines the sort
    order for the table. This patch adds a directional indicator that let
    users know which column(s) is being sorted and the direction of the
    sort.

    known issue: because sorting indicator is a background image, it will
    appear below column name if the name is too long.

    Change-Id: If7194728d4335a04e9e8a7becd0086e2d3dc4b67
    Closes-Bug: #1279578