Grate shake refactor

The grate shake logic has been restructured.
* Changes in motor state are now immediate, eliminating a delay of one
control cycle that caused the grate to shake for longer than expected.
* Grate shake length is now specified in .1 second increments.
* Reduced dependencies on global variables
Increased lambda setpoint precision

Lambda setpoint precision has been incread to 0.0025 from 0.01.  The
lambda tuning display code has been updated to reflect this change.