Needs testing

Code compiles for both RigidPanel LCD and RepRap Discount Full Graphic LCD, but needs testing.  Difference between our fork and mainstream Marlin are now reduced to:
Modified files:
cardreader.cpp
	-- added support for slower SD card speeds
Configuration.h
	-- Motherboard 42 for RigidBot
	-- PID values for RigidBot hot end
	-- Build volumes for RigidBot models
	-- Added Y_CENTER_POS and Y_CENTER_POS for LCD "move to center"
	-- "STEPPER_RESET_FIX" to keep stepper drivers disabled until voltage stabilizes
	-- "RIGIDPANEL" LCD support
Configuration_adv.h
	-- Fixed typo for smaller block buffer size when SD card support is enabled
language.h
	-- Machine name for RigidBot
	-- USB vs Standard LCD Menu Messages
Makefile
	-- Added support for u8glib compiling from command line
	-- Hardware variant for RigidBot
	-- ultralcd vs rigidpanel distinction
Marlin_main.cpp
	-- Optional STEPPER_RESET_FIX
pins.h
	-- Motherboard 42 pins
Sd2Card.cpp
	-- Longer wait for response from SD card command
SdFatConfig.h
	-- Increase maximum filename length

New files:
LiquidCrystalFast_Mod.cpp
LiquidCrystalFast_Mod.h
rigidpanel.cpp
rigidpanel.h
ultralcd_implementation_RigidPanel.h
example_configurations/rigidbot/
	-- With all our machine-unique parameters