Added immersive mode to App Settings fullscreen mode

Closes #17
Workaround to enable DPI changes for SystemUI on KitKat

Finding which packages are really started in the current process (not
including things like createPackageProcess() etc.) is pretty hard.
I use this workaround for a common use-case for now, but hope to find a
better way in the future (which should then be available as API in the
framework).