message: SerialManager_UI: add method for default GUI page
diff: #define SerialManager_UI_h
  #include <Arduino.h> //for String
  +#include <TympanRemoteFormatter.h> //for TR_Page
  //#include "SerialManagerBase.h"
  class SerialManagerBase; //forward declaration
  @@ -23,6 +24,9 @@ class SerialManager_UI {
  virtual void setFullGUIState(bool activeButtonsOnly=false) {}; //default is to do nothing
  // ///////////////////////
  + //create the button sets for the TympanRemote's GUI, which you can override
  + virtual TR_Page* addPage_default(TympanRemoteFormatter *gui) { return NULL; }
  +
  // predefined helper functions, which you can override
  virtual String getPrefix(void) { return String(quadchar_start_char) + String(ID_char) + String("x"); } //your class can use any and every String-able character in place of "x"...so, you class can have *a lot* of commands
  