Display Filament Sensor data on 20x4 LCD

Changes to support displaying the real-time filament width and the
volume factor on a 20x4 LCD.  The data is displayed on the 4th line.
First the status message is displayed for 5 seconds, and then the
filament data is displayed.  The status message can be seen by
re-selecting the info screen in the menu.
Display Filament Sensor data on graphic LCD

Added support to show the filament width on the status line of the
graphic LCD.  The status will show for 5 sec and then switch over to
data.  Status can be seen by clicking the button.
Added Filament Sensor to the README

Added some background on the filament sensor to explain it better.