Legacy gradient mode

In previous versions, when the KitKat fake gradient wasn't enabled, the gradient would still show for apps that use the KitKat API.
In newer versions, we added our own overlays (none, gradient, semi-transparent), selecting none would completely disable the gradient, even in apps that used the API.

While this may be expected behavior for most users, it might look bad on apps that show lists behind the system bars. Legacy mode restores the old behavior.