Add a system shortcut to toggle dark mode

[simjnd]

Problem

The need for dark mode is not necessarily tied to sun cycle: you can wake up and start working after the sun has risen, but not be ready yet for blasting your eyes with the white screen and toggling appearance mode manually currently takes 4 clicks (open Settings -> click Desktop -> click Appearance -> click Dark)

Proposal

Add an entry "Toggle dark appearance" to which I could bind a shortcut like Super + D to easily switch between dark and default mode.

Prior Art (Optional)

No response

[cassidyjames]

I think this would also require listening to the keyboard shortcut in Gala; I've filed this companion issue: https://github.com/elementary/quick-settings/issues/30

[janxkoci]

Note that you can search for "dark" in app menu (slingshot) to get to the settings a little faster.