Implemented an I2C LCD display and controller

New file: ultralcd_implementation_panelolu2.h is an extension of ultralcd_implementation_hitachi_HD44780.h
Edited:
Marlin.pde to include the wire library and Lincomatic's LiquidTWI2 library if PANELOLU2 is defined
pins.h to define the click switch and SDSS pins for Melzi and Sanguinololu
ultralcd.cpp to include the correct lcd_implementation header
Configuration.h to add PANELOLU2 as as display and controller option.