Move Sud step's target temperature from ramp.temp to step.temperature

A step's target temperature applies to the whole step (it's what a
ramp ramps to and what a hold then holds at), not just its ramp phase
- promote it from a nested "ramp": {"temp": ...} to a step-level
"temperature" field, defaulted like descr/grain_mass/etc. Updates all
consumers (Sud._build_step, SudTask, the GUI's forecast estimator,
demo_sud.py) and migrates sude/sud_0010.json and the README.

tasks/sud.py

@@ -69,13 +69,13 @@ class SudTask(ATask):
 		# bool(...): get_theta_ist() can be a numpy.float64 (Pot's transport
 		# delay line is a numpy array internally) - the '<' comparison would
 		# then yield numpy.bool_, which json.dumps() can't serialize.
-		cooling = bool(ramping and ramp is not None and ramp['temp'] < self.tc.get_theta_ist() - TEMP_REACHED_TOLERANCE)
+		cooling = bool(ramping and ramp is not None and step['temperature'] < self.tc.get_theta_ist() - TEMP_REACHED_TOLERANCE)
 		self.tc.set_cooling(cooling)
 
 		if step is not None:
 			self.apply_plant_params(step)
 			if ramping and ramp is not None:
-				self.tc.set_theta_soll(ramp['temp'])
+				self.tc.set_theta_soll(step['temperature'])
 				self.tc.set_heatrate_soll(ramp['rate'])
 			self.apply_stirrer(phase)
 
@@ -83,7 +83,7 @@ class SudTask(ATask):
 			'Index': self.sud.index,
 			'Type': 'ramp' if ramping and ramp is not None else 'hold' if hold is not None else None,
 			'Descr': step.get('descr') if step else None,
-			'Temp': ramp.get('temp') if ramp else None,
+			'Temp': step.get('temperature') if ramp is not None else None,
 			'Rate': ramp.get('rate') if ramp else None,
 			'Duration': hold.get('duration') if (hold is not None and not ramping) else None,
 			'WaitForUser': step.get('user_wait_for_continue', False) if step else None,