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Add device reporting section to the management page. Clean-up related C++ backend.
Apply text changes, add images.

Bug: 879146
Change-Id: I50d65fabfb5cf7acf55a9f444794bcf8c34b8d3f
Reviewed-on: https://chromium-review.googlesource.com/c/1470796Reviewed-by: Thiemo Nagel <tnagel@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Roman Aleksandrov <raleksandrov@google.com>
Cr-Commit-Position: refs/heads/master@{#635966}