Update hard keyboard setup notification.

Starting from Android N, Settings.ACTION_HARD_KEYBOARD_SETTINGS is
available for navigating users to hardware keyboard settings.  We should
use this for keyboard layout notification.

This CL also updates the notification title and message based on
feedback from UX writing team.

Bug: 27795350
Change-Id: Ic93075f933d47486644092c469d7a3517eb2e541