hw: re-add priority down-scaling

ref #960
fixup: fix semantic of scale_priority
related to commit 5a42f40f04981581327639a75298e9e653ef39f5
ref #961
Variant of nit_fb with fading effect
Add nano3d and crystals demo
demo: Utility for animating values
demo: Graphical menu application
demo: Background images
Disable sound in menu, as well as banners, and hiding
fade_fb: change alpha blending gradient
i.MX53 tablet vmm: implement input, framebuffer, GUI
quirk to circumvent issue #956