Adjust Z0 menu with "Set Z0 here", enabling convenient Z end stop adjustment in firmware. 

Hi,
I am not familiar with Git and this is my first pull request.
Also, I am not sure what the procedure is regarding all the customisation changes that are made as a matter of course in configuration.h and configuration_adv.h.

The change in temperature.cpp is unrelated to this feature, but I think important, since I was unable to PID tune my E3D without it because the heater was too powerful and triggered the abort  every time.

Regards,
Kit