Screen Lock Feature
This only shows the settings if the feature is available. If it is available, but no device screen lock is set, the setting will be disabled with a different summary. If the setting is activated, it shows a drawer item for locking. Once locked, the screen lock secret needs to be entered to enter the app again. The foreground notification is updated depending on the lock state.
First part of #1247 (closed)
(Entering the lock pin isn't shown since it is a secure screen.)