Add an enable/disable switch for the temperature controller

New TempControllerBase.enabled (default False) forces y=0 in
process_pid() when off, same mechanism as the existing cooling
override - the controller tries not to drive the heater at all.

tasks/tempctrl.py: new 'Enable' recv command and 'Enabled' broadcast
on the TempCtrl channel. tasks/sud.py: SudTask now enables the
controller on any non-IDLE/DONE Sud state and disables it (forcing
power back to 0) on IDLE/DONE, so automatic mode owns it for the
duration of a run and hands back manual control once it stops/finishes.

gui: new "Enabled" checkbox on the Manual tab's Controller group,
synced from the server; the temp/heatrate setpoint controls are
disabled whenever the controller itself is disabled.

tasks/tempctrl.py

@@ -35,6 +35,10 @@ class TcTask(ATask):
 	def on_rate_ist_changed(self, value):
 		asyncio.create_task(self.send({'Ist': {'Rate': value}}))
 
+	def on_enabled_changed(self, value):
+		print("Enabled change to {}".format(value))
+		asyncio.create_task(self.send({'Enabled': value}))
+
 	async def recv(self, msg):
 		print(msg)
 		for key in msg.keys():
@@ -45,6 +49,8 @@ class TcTask(ATask):
 						self.tc.set_theta_soll(submsg['Temp'])
 					if 'Rate' in subkey:
 						self.tc.set_heatrate_soll(submsg['Rate'])
+			if 'Enable' in key:
+				self.tc.set_enabled(bool(msg['Enable']))
 
 	async def send(self, data):
 		await self.msg_handler.send(data)
@@ -58,9 +64,11 @@ class TcTask(ATask):
 		self.tc.set_on_changed('theta_soll_set', ChangedFloat(self.on_temp_soll_changed, prec=1).set)
 		self.tc.set_on_changed('heatrate_soll', ChangedFloat(self.on_rate_soll_curr_changed, prec=1).set)
 		self.tc.set_on_changed('heatrate_soll_set', ChangedFloat(self.on_rate_soll_set_changed, prec=1).set)
+		self.tc.set_on_changed('enabled', self.on_enabled_changed)
 
 		self.tc.set_theta_soll(20.0)
 		self.tc.set_heatrate_soll(1.0)
+		await self.send({'Enabled': self.tc.enabled})
 
 		while True:
 			self.tc.process()