First v0.1 tests and fixes

Optimized load reading, fixed battery readings, fixed load cell
calibration routine, added ability to change PWM frequency, added
command to write all values to EEPROM (previously was done any time
something changed), broke out main loop delta time for display.

Need to test calibration routine - chooses correct value but haven't
tried to actually put a weight on the scale.

To do: allow user to manually enter calibration data (skip actually
measuring if re-entering old calibration).
To do: set up analog ports differently