Make input screen black to save battery life

[AutoImport-azhao12345]

On the Note 1 and 3, and others, they use amoled screens, which draw less power when displaying black. There should be an option to change the color of the input screen.

[AutoImport-fredrikchabot]

Seccond

[AutoImport-FatihBAKIR]

Added an option to use a darker color

https://github.com/rfc2822/GfxTablet/pull/76