Review and Merge RevarLCD code

[jmil]

Review and Merge RevarLCD code. He modded v2.0 BETA 2 for LCD with accompanying 16-button keypad support. I merged with master and made one additional change to update it.

[jmil]

correction: Revar modded v1.8 with HBP support. Adam says he will merge these changes with v2.0 BETA 2 since so much has changed and documentation on the new v2.0 rewrite is still being worked on.

[makerbot]

Changing to 2.1 release (est. late April) so we don't block the 2.0 release on this

[revarbat]

I've ported the RevarLCD code to v2 in the RevarBat/G3Firmware fork, master branch. It runs well, but there is currently a firmware crasher but that occurs after a few dozen minutes printing.

[revarbat]

The RevarLCD branch is only useful with the Gen3 hardware. The Gen4 hardware is incompatible with I2C. I've moved on to Gen4 hardware, myself, and am currently modifying the stock Gen4 Interface kit menus to get the same functionality. I'm calling RevarLCD dead.