config: disable animations and key preview popups when using DirectFB

DirectFB/framebuffer uses sw rendering and is super slow on most devices that are trying to run osk-sdl. This disables animations (wavy dots...) and key preview popups when the renderer is DirectFB to help make osk-sdl more responsive for devices that don't have hw accel support.

The second patch in this MR adds a tooltip that shows a message to the user when animations are disabled that the app is trying to unlock the disk.