Add "About Printer" information menu.

Includes:
  *firmware version / branch / date.
  *extruder count
  *board information (name, serial details, power supply type)
  *thermistors (names, min/max temperatures)
  *printer statistics (PRINTCOUNTER details)

Thanks to @thinkyhead for contributions.

Marlin/printcounter.h

@@ -131,6 +131,12 @@ class PrintCounter: public Stopwatch {
      */
     void showStats();
 
+    /**
+     * @brief Return the currently loaded statistics
+     * @details Return the raw data, in the same structure used internally
+     */
+    printStatistics getStats() { return this->data; }
+
     /**
      * @brief Loop function
      * @details This function should be called at loop, it will take care of