Display filament sensor data on a 20x4 LCD or Graphical LCD

Supports displaying filament sensor data on either a character 20x4 or graphical LCD.  Because nearly all the LCD real-estate is taken the code uses the status area to display the data.  The status will display for 5 seconds, and then be replaced by the data display.  To see the status again, press the knob to select the menu again.  Also, if the status message is updated, it will display for 5 sec.  A #define in the config file is used to enable the display.

I also added some background explanation to the readme about the filament sensor input.