- Show units on lightweight status screen.
- Fixed progress bar so it works with M73

- This status screen uses the ST7920 character generator to greatly
  reduce SPI traffic and MCU load when updating the status screen.

- Has been tested with the RepRapDiscount Full Graphics Smart Controller
  but should work with any LCD that uses an ST7920 or fully compatible
  controller.

- Also deleted old implementation files which had been renamed.