Use the dark theme of toastify when running dark mode
react-toastify v8 has a way to customize the look of a toast quite easily: https://github.com/fkhadra/react-toastify/releases/tag/v8.0.0
Would be nice to use the dark theme when we're using Kresus' dark theme, e.g.
toast("hello", {
type: "dark"
});
We could maybe use a react context to avoid drilling down the theme info all the time, btw.