Notification toggle section (2/3).

Section for toggling the "show/hide notifications on the lock screen"
seetting.

Fixes: 265436567
Test: unit tests included
Test: manually verified that it toggles the setting
Test: manually verified that the setting in Settings > Display > Lock
screen > Privacy is changed to match

Change-Id: I76956eba5ae77a6f9bdd551f7043fa725f4b0fe9