Changing dark/light mode on dark theme
Solves issue #206 (closed)
This commit allows the user to change light/dark modes even using a dark theme (which was possible only on light theme). It uses the GTK themes defined in default_themes in the theme.py
file. For unknown theme it defaults to Adwaita.
I think Adwaita is installed by default on Gnome, otherwise the Theme
class should be extended to detect the current theme, eventually see if a ...-dark
theme is available.