[Feature Request] Add option to use system theme

[vherrmann]

Now with the introduction of the light mode, i would love session to switch between dark and light side dependent on my system's theme.

[ghost]

Just as a reminder, it would be great for this to work on both windows and linux

[KeeJef]

If you are working on this as a good first issue

Please use the same copy from mobile in the Settings menu:

Setting Header: Auto night-mode
Copy: Match system settings

Location: Between Themes and Zoom Factor in Appearance
Toggle & Padding: As per settings in Permissions

[KeeJef]

Added