[UX6] G8 Black Theme for V20 G

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Version 2.1:
- Improve theme in low resolution devices.
Version 2.01:
- Improve slider thumb size.
Version 2.0:
- Bring G8 style to theme.
- If you like G8 wallpaper, you can get it from https://goo.gl/6ujqWU.
- I have also updated navigation button patch (Galaxy S10, Pixel 3)