Fixed bugs where TargetZ, Bed Temp, Extruder Temps, Retract Feed Rate and Retract Length weren't properly considered as floats. Now capable of properly targeting decimal Z values, and altering others as decimals
Updated debug cases to test for it.
Added comments.
Added support for changing Retract Length and Speed.
Applied code refactoring to clean up various coding styles.
Broke up functions for clarity.
Fixed issue of cumulative ChangeZ mods so they can now properly be stacked on top of each other.
Removed layer spread option in favor for fixing ChangeZ stacking
Split up class so it can be debugged outside of Cura.
This potentially set the flow rate to -1, since it was changing the flow rate to the old['flowrateTwo'] which was left at -1 since initialisation because it didn't update here.
