Truly allows admins/managers to hide/show assignedto/department columns

This builds on issue #482 where it adds the ability to show/hide the department column in open tickets.

This fix allows admins/managers to truly hide the assignedto/department column by their preferences.  The scenario it fixes is below

* Before
 * Global Assigned To: ON
 * Personal Pref.: OFF
 * Column Still showed
* After
 * Global Assigned To: ON
 * Personal Pref.: OFF
 * Column no longer shows