preliminiary implementation for the early heating finish.

Might be replaced by something more clever, e.g. by erik, and does not yet support the second extruder or the bed.
its kind of not so cool, because you need 6 more ints.
Maybe isheating() should use the degrees directly, as it is not used in time-critical anyways.
Then it would be much easier. to have the offsets without additional variables.

Marlin/temperature.cpp

@@ -43,6 +43,8 @@
 //===========================================================================
 int target_raw[3] = {0, 0, 0};
 int current_raw[3] = {0, 0, 0};
+int heatingtarget_raw[3]= {0, 0, 0};
+
 
 #ifdef PIDTEMP