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/pins_PRINTRBOARD.h

@@ -35,6 +35,7 @@
   #error "These Printrboard assignments depend on traditional Marlin assignments, not AT90USBxx_TEENSYPP_ASSIGNMENTS in fastio.h"
 #endif
 
+#define BOARD_NAME         "Printrboard"
 #define LARGE_FLASH        true
 
 // Disable JTAG pins so they can be used for the Extrudrboard