Implement dark mode theme (#744)

Co-authored-by: DevilXD <4180725+DevilXD@users.noreply.github.com>

translate.py

@@ -161,6 +161,7 @@ class GUISettingsGeneral(TypedDict):
     autostart: str
     tray: str
     tray_notifications: str
+    dark_mode: str
     priority_mode: str
     proxy: str
 
@@ -361,6 +362,7 @@ default_translation: Translation = {
                 "autostart": "Autostart: ",
                 "tray": "Autostart into tray: ",
                 "tray_notifications": "Tray notifications: ",
+                "dark_mode": "Dark mode: ",
                 "priority_mode": "Priority mode: ",
                 "proxy": "Proxy (requires restart):",
             },