Improved the behaviour of the setpoint setting with the rotary encoder.
The setpoint is now double buffered which means that while changing the
setpoint the actual controller setpoint is unaffected. The change will
only be visible to the controller when the setpoint button is released.
At that time the controller integrals are now also reset (but only when
necessary).
In addition rounding is performed to the closest multiple of the
encoder temperature increment. The setpoint is now also limited between
-50 and 50 degrees Celsius (but only for encoder operation).