Design and implement dark mode CSS

[pedromvpg]

https://bisq.wiki/MediaWiki:Darkvector.css

[wiz]

https://bisq.wiki/MediaWiki:Darkvector.css

This theme was taken from https://github.com/dolfinus/DarkVector

In our repo the theme resides at https://github.com/bisq-network/wiki/tree/master/skins/DarkVector

If you're going to design and implement a proper dark mode maybe make a new theme from the light theme you designed, instead of using that