Update TempControlSystem_Main

This is working!

Future functionality: 
      (1) Improve PID using AutoTune.  It wavers around set point.  I watched it for ~10 min and saw it go from above, to below, to perfect, to a little too high again.  It definitely gets better over time.  It seems to heat really slowly--not sure which PID coefficient needs to be changed in order to make that faster...
      (2) Set alarm lock if the heater has beeen on for too long 
          > because if physical thermocouple fails, currentTemp is unreliable.
      (3) Other safety features