Allow Edit menu to call fn after edit; Fix PID Ki and Kd display in menus; Actually use changed PID and Max Accel values

Add new 'callback' edit-menu types that call a function after the edit is done. Use this to display and edit Ki and Kd correctly (removing the scaling first and reapplying it after). Also use it to reset maximum stepwise acceleration rates, after updating mm/s^2 rates via menus. (Previously, changes did nothing to affect planner unless saved back to EEPROM, and the machine reset).

Add calls to updatePID() so that PID loop uses updated values whether set by gcode (it already did this), or by restoring defaults, or loading from EEPROM (it didn't do those last two). Similarly, update the maximum step/s^2 accel rates when the mm/s^2 values are changed - whether by menu edits, restore defaults, or EEPROM read.

Refactor the acceleration rate update logic, and the PID scaling logic, into new functions that can be called from wherever, including the callbacks.

Add menu items to allow the z jerk and e jerk to be viewed/edited in the Control->Motion menu, as per xy jerk.
Provide smoothed, rotation-speed-sensitive adjustment of speed multiplier on LCD main status screen.

Monitor movements in the encoder wheel over a period of time; reduce the sensitivity at slow speeds (so that you can accurately change it in single steps, and not accidentally change it), while moving in larger increments for faster turns.
Make the encoder position a signed variable, since most of the logic that uses it assumes that it is (and then works around the fact that it isn't).