plugin: rafaelmardojai/thunderbird-gnome-theme support

[TheGreenGuy5]

Plugin description

Support for https://github.com/rafaelmardojai/thunderbird-gnome-theme, similar to firefox-gnome-theme support.

Additional Context

No response

Did you read the Code of Conduct?

• I have read the Code of Conduct.

[qwertychouskie]

I suspect it would make more sense to add the functionality to the existing Firefox plugin rather than make a while separate plugin. You can already use the customChrome.css made by the Firefox plugin in Thunderbird, and it works, though it's missing a couple values (I had to add --gnome-view-background and --gnome-window-background).