advance and ultipanel not any more in default config

- The temperature control is pretty much complete
  (not sure what to do w/ autotemp though)
  Changed the pins assignment to clearly separate bed and extruder heaters
  and temp sensors, changed a bit how termistor tables are handled.
- The steppers control is rudimentary
  (only chanages what pins it uses depending on the active_extruder var,
   but that's enough for switching extruder in the start.gcode in the
   the profiles)
- Tested only w/ RAMPS 1.4

Found a couple of unused variables, that I commented.
Tried to solve the program memory warning message, and failed.