Add user-toggleable setting to turn off display between refreshes, which helps mitigate the sunlight fading issue on e-ink displays. Changes: - Add turnOffScreen parameter to HalDisplay methods - Add fadingFix member and setFadingFix() to GfxRenderer - Add fadingFix setting to CrossPointSettings with persistence - Add "Sunlight Fading Fix" toggle in Display settings - Update SDK submodule with turnOffScreen support