Add dark theme for Android 10

[SpiritCroc]

Imported from my Substratum theme
https://github.com/SpiritCroc/DarkCroc-Android-theme

[luca020400]

Thanks, last time I talked with Jorge he wanted the app to stay "white".
This forces the app to follow system theme, and I'm sure he would prefer a toggle for that instead.

[SpiritCroc]

Right, adding a toggle shouldn't be hard, I can do that if @jruesga wants

[jruesga]

@SpiritCroc so sorry for so much delay to replay you.

TBH, I don't like to much Dark Themes in general, but if there is a good dark theme I won't opposite to merge it. Anyway, I tested your PR and I think there is still a lot of things to theme. This repo (https://github.com/Mazda--/rview/commits/master) contains more progress on top of your work, but I'm still feeling that, in both cases, many of the dark colours are not fitting properly in the screen (too really brighter and not matching with the background).