update column headers when dragging columns around
update column headers when dragging columns around

fixes CNVS-35474

test plan:
* visit Gradezilla
* drag columns around
* ensure column headers always display intended text

Change-Id: I4de75c0cad7eccc837fb9d6a343a74bae31373f6
Reviewed-on: https://gerrit.instructure.com/105895
Reviewed-by: Keith T. Garner <a1a80143a840c140f31c3495ebbd9ec906e09fed@instructure.com>
Tested-by: Jenkins
QA-Review: Anju Reddy <851202533fb1f0b615e4547ba226c76996d060dd@instructure.com>
Product-Review: Keith T. Garner <a1a80143a840c140f31c3495ebbd9ec906e09fed@instructure.com>

instructure/canvas-lms,venturehive/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,venturehive/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,venturehive/canvas-lms,instructure/canvas-lms,venturehive/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,djbender/canvas-lms,djbender/canvas-lms