Add settings customize Discord status text

The new settings let you customize the "Listening to" status text, according to the [status display types](https://discord.com/developers/docs/events/gateway-events#activity-object).

Fixes #1796.

src/discord/richpresence.h

@@ -70,6 +70,7 @@ class RichPresence : public QObject {
   };
   Activity activity_;
   bool initialized_;
+  int status_display_type_;
 };
 
 }  // namespace discord