open twitch usercard on middle mouse (#1669)

Co-authored-by: pajlada <rasmus.karlsson@pajlada.com>

src/util/Twitch.hpp

@@ -0,0 +1,9 @@
+#pragma once
+
+#include <QString>
+
+namespace chatterino {
+
+void openTwitchUsercard(const QString channel, const QString username);
+
+}  // namespace chatterino