Minor eeprom improvements

* Eeprom version increases from V(10,11,12) to V13
* Remove need for multiple eeprom versions - space used by optional
parameters (notably delta and scara parameters, ultipanel preheat
parameters) is skipped (written to 0.0 on write, skipped on read) where
not needed, leaving other variables in fixed locations. This has no
real-world implication, but avoids use of three eeprom version numbers
for each subsequent change of eeprom structure.
* Add bed pid parameters to eeprom if PID is enabled for the bed