allow customizing twitch server parameters through environment variables (#1449)

src/common/Env.hpp

@@ -14,6 +14,9 @@ public:
     const QString recentMessagesApiUrl;
     const QString linkResolverUrl;
     const QString twitchEmoteSetResolverUrl;
+    const QString twitchServerHost;
+    const uint16_t twitchServerPort;
+    const bool twitchServerSecure;
 };
 
 }  // namespace chatterino