[App Management] Add router.

This CL sets up routing for the app management page. It also adds an
action and a reducer to handle changing to a different subpage within
the app management page.

Bug: 906508
Change-Id: I5b877cc7aed66c7626045d08066bac9ccc59b5d2
Reviewed-on: https://chromium-review.googlesource.com/c/1381356
Reviewed-by: calamity <calamity@chromium.org>
Reviewed-by: Eric Willigers <ericwilligers@chromium.org>
Commit-Queue: Reka Norman <rekanorman@google.com>
Cr-Commit-Position: refs/heads/master@{#618133}
20 files changed