GitLab

This CL adds:
- Polymer template for all the screens of the UI
- Shared styles for all the screens
- Button templates and behaviors
- Error screen
- Network offline screens

Also:
- UI behaviors and event handler implementation to enable the flow to operate.
These are mostly in:
chrome/browser/resources/chromeos/edu_coexistence/edu_coexistence_ui.js
chrome/browser/resources/chromeos/edu_coexistence/edu_coexistence_app.js

But there are smaller bits of functionality in the other js files as
required by their respective screens.

Bug: 1133828,1133827,1123218
Change-Id: I297fe1a5c18bb3806d94b4c5e635c0dd4a990f70
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2462673Reviewed-by: Ted Choc <tedchoc@chromium.org>
Reviewed-by: Aga Wronska <agawronska@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Dan S <danan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820844}