set focus when switching between app center and external apps views

fixes PLAT-582

test-plan:
when you click "View App configurations" it should set focus to the "View App Center" and visa versa

Change-Id: I6fc2b2b9b2a7435bb7853ecfb99d7ef4523e4a5b
Reviewed-on: https://gerrit.instructure.com/38776
Reviewed-by: Brad Humphrey <brad@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>
Product-Review: Nathan Mills <nathanm@instructure.com>