[macOS] Use the dark theme when the dark mode is used

When the dark mode is used, the dark theme should be set on the application too.

First, the Info.plist must be updated to tell the OS that the app supports the dark mode:

<key>NSRequiresAquaSystemAppearance</key>
<string>false</string>

Optionally, we need to find a way to make the switch between default <-> dark them when the user change for/from the dark while the app is running.