Add visual styling to roles table at admin/config/people/taxonomy_access

This issue is a followup to #1314586: Add status column to admin/config/people/taxonomy_access and #1314606: Redesign role configuration page.

See http://xjm.drupalgardens.com/sites/xjm.drupalgardens.com/files/1_main_sc.... Once the roles table at admin/config/people/taxonomy_access is changed, it would be nice to add css classes to make the table easier to understand. We might use the gear cog icon from admin/modules for the configure link.

We could also use misc/message-16-error.png and misc/message-16-ok.png to illustrate when roles are enabled or disabled.