use the same column headers in visible and screenreader headers
use the same column headers in visible and screenreader headers

test plan:
 - in the analytics table view, ensure screenreaders read
   the same column headers as are visible
   (previously they read the field name instead of the
    column header text, "title" instead of "Assignment",
    "onTime" instead of "On Time", etc.)

fixes CNVS-29539

see also
https://github.com/jstanley0/react-bootstrap-table/commit/21d1660d1b2a42acfe2a7ba54d27ba33ebf26421

Change-Id: I2d1a9e6d40c69d734334475ba6577cf1ec1dcfa5
Reviewed-on: https://gerrit.instructure.com/80838
Tested-by: Jenkins
Reviewed-by: Clay Diffrient <9dff2e5c98626d20d2848250c411e8009465bb87@instructure.com>
QA-Review: Deepeeca Soundarrajan <5bcd4b623f00b7fc2942cd1c65c245b30a48a61f@instructure.com>
Product-Review: Jeremy Stanley <b3f594e10a9edcf5413cf1190121d45078c62290@instructure.com>

instructure/analytics,SwinburneOnline/canvas-analytics,instructure/analytics,SwinburneOnline/canvas-analytics,SwinburneOnline/canvas-analytics,beyond-z/analytics,beyond-z/analytics,beyond-z/analytics,instructure/analytics