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This reverts commit f8a8c0d8.

This only shows the settings if a screen lock is available.
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.

First part of #1247

This gets rid of all those pesky 9-Patch drawables

This fixes an issue where the build type values were overriding the
flavor values.

Also change the logo to a logout icon

This is done via another preference in the settings screen
and an action button attached to the notification itself

Fixes #888.