Implement custom "Lock screen behavior"

This option enables or disables Hover notifications on
lock screen.

Default behavior of Hover notifications is to show on
insecure lock screen and not to show on secure lock screen.

Now, Hover notifications can be shown on:
- Both secure and insecure lock screen
- Neither secure nor insecure lock screen
- Insecure lock screen only (default behavior)

Signed-off-by: Shubhang Rathore <shubhang92@gmail.com>