Add a button to switch to/from dark mode

[Binnette]

Hello, my windows computer is configured to be in dark mode. So the map always show in dark mode.

And sadly, the dark mode need more love to be more readable:

That's why we need a button to allow users to switch from dark mode to light mode. To make the "priceless map" beautiful and readable again ❤️

[ToastHawaii]

Switching between dark, light and system mode is now supported. :)