Feat: Black (AMOLED) theme

[xMate420x]

I think a fully black theme is really useful for AMOLED devices, as it can save a lot on battery, and in my opinion looks better than regular dark. I will also write a separate installer for it later today.

[lkd70]

I'm a huge fan of this idea, I too love a fully black amoled-compatible theme. The reason I've not incorporated such a theme already is simply because it doesn't always look as nice on a desktop, which I feel is likely the main platform that pihole would be used from. Having said that, it'd not be hard to make a theme selection option available in the installer. What are your thoughts on that? Though keep in mind there's a lot more things that I need to rewrite before doing that (I need to submit some PR's to the official pihole repo in order to remove some statically-themed elements)