Added BlinkM support over i2c

Reason I made this is to get visual feedback from the bot using LEDs. In my case RGB LEDs illuminate the housing of the printer and show its status (preheating/homing/printing/tool change/layer change/cooldown/etc.) based on the color. 

Addinitional hardware required is a BlinkM module connected to the i2c bus of the bot (and LEDs connected to the BlinkM module). I have tested this with a RAMPS 1.4 board and a BlinkM MaxM module.