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/constants/notificationssettings.h

@@ -71,6 +71,14 @@ constexpr char kSettingsGroup[] = "DiscordRPC";
 
 constexpr char kEnabled[] = "enabled";
 
+constexpr char kStatusDisplayType[] = "StatusDisplayType";
+
+enum class StatusDisplayType {
+  App = 0,
+  Artist,
+  Song
+};
+
 }  // namespace
 
 #endif  // NOTIFICATIONSSETTINGS_H