Multiple fixes

- compile time button configuration #3792
- remove IR config if not compiled
- additional string optimisations

wled00/fcn_declare.h

@@ -434,6 +434,7 @@ void handleSerial();
 void updateBaudRate(uint32_t rate);
 
 //wled_server.cpp
+String getFileContentType(String &filename);
 void createEditHandler(bool enable);
 void initServer();
 void serveMessage(AsyncWebServerRequest* request, uint16_t code, const String& headl, const String& subl="", byte optionT=255);