Create a basic doze dream in SystemUI.

The doze dream is not configured by default.

When configured, the doze dream does not show anything by default.
It teases a dark version of the keyguard (showing only the time
and notifications) when a notification arrives or significant motion
is detected.

Bug:15863249
Change-Id: Icfceb054d35d6fd4d9178eda7480e2464873ca4b