Add a "Pot reset to ambient temperature" button, sim-only

New btn_pot_reset next to the ambient entry, sends {"Pot": {"Reset":
true}}; tasks/pot.py's PotTask.recv() (previously a no-op) now resets
the plant to its current ambient temperature (Pot.initial()) on that
command.

The button only appears when the server reports its Pot is simulated
(new "PlantSim" field on the System channel, derived from
config.json's previously-unused Controller.plant_name) - resetting a
simulated plant's temperature is meaningless for a real one.

client/brewpi_gui.py

@@ -330,6 +330,10 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 		self.checkbox_heater_activate.stateChanged.connect(self.on_checkbox_changed)
 		self.checkbox_stirrer_activate.stateChanged.connect(self.on_checkbox_stirrer_activate_changed)
 		self.lineEdit_ambient.returnPressed.connect(self.on_ambient_entry_changed)
+		self.btn_pot_reset.clicked.connect(self.on_action_pot_reset)
+		# Only meaningful (and only shown) once the server confirms its Pot
+		# is simulated - see on_system_changed()'s "PlantSim" handling.
+		self.btn_pot_reset.setVisible(False)
 
 		self.send_data = Queue()
 		self.slider_pwr_initial_update = True
@@ -462,6 +466,7 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 			self.sud_user_message = None
 			self.ambient_temp = None
 			self.lineEdit_ambient.clear()
+			self.btn_pot_reset.setVisible(False)
 			self.warp_factor = 1.0
 			self.sud_start_time = None
 			self.sud_paused_total = 0.0
@@ -500,8 +505,13 @@ class Window(QtWidgets.QMainWindow, Ui_MainWindow):
 					self.lineEdit_ambient.setText("{:.1f}".format(self.ambient_temp))
 			elif "WarpFactor" in key:
 				self.warp_factor = msg['WarpFactor']
+			elif "PlantSim" in key:
+				self.btn_pot_reset.setVisible(msg['PlantSim'])
 		self.update_status_env_label()
 
+	def on_action_pot_reset(self):
+		self.msg_pot.send({'Reset': True})
+
 	def on_ambient_entry_changed(self):
 		try:
 			value = float(self.lineEdit_ambient.text())