Add deprecation notification when supervised user manager logs in

Also:
Change the Window Disposition for the link opened from the
Learn More link to NEW_WINDOW.  When there is no existing
window available, opening the link  with the SINGLETON_TAB disposition
results in a crash.

Hide the login screen Supervised Users deprecation warning notice
when a non-supervised user is selected.

Bug: 916799
Change-Id: I6a1642542b654712cb9bdc066687dc6818cd3ee7
Reviewed-on: https://chromium-review.googlesource.com/c/1389498
Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Reviewed-by: Michael Giuffrida <michaelpg@chromium.org>
Commit-Queue: Danan S <danan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621739}
3 files changed