Control Panel: Move postfilter into its own group

The postfilter is an aspect of the sampling ADC on the Thermostat, and
not the connected thermistor.

pythermostat/pythermostat/gui/view/ctrl_panel.py

@@ -201,13 +201,13 @@ class CtrlPanel(QObject):
                     "Output Config", "Control Method", "Set Current"
                 ).setValue(settings["i_set"] * 1000)
                 if settings["temperature"] is not None:
-                    self.params[channel].child("Temperature").setValue(
+                    self.params[channel].child("Readings", "Temperature").setValue(
                         settings["temperature"]
                     )
                     if settings["tec_i"] is not None:
-                        self.params[channel].child("Current through TEC").setValue(
-                            settings["tec_i"] * 1000
-                        )
+                        self.params[channel].child(
+                            "Readings", "Current through TEC"
+                        ).setValue(settings["tec_i"] * 1000)
 
     @pyqtSlot(list)
     def update_thermistor(self, sh_data):
@@ -244,9 +244,9 @@ class CtrlPanel(QObject):
         for postfilter_params in postfilter_data:
             channel = postfilter_params["channel"]
             with QSignalBlocker(self.params[channel]):
-                self.params[channel].child(
-                    "Thermistor Config", "Postfilter Rate"
-                ).setValue(postfilter_params["rate"])
+                self.params[channel].child("Postfilter Config", "Rate").setValue(
+                    postfilter_params["rate"]
+                )
 
     def update_pid_autotune(self, ch, state):
         match state:

pythermostat/pythermostat/gui/view/param_tree.json

@@ -1,17 +1,23 @@
 {
    "ctrl_panel": [
       {
-         "name": "Temperature",
-         "type": "float",
-         "format": "{value:.4f} °C",
-         "readonly": true
-      },
-      {
-         "name": "Current through TEC",
-         "type": "float",
-         "suffix": "mA",
-         "decimals": 6,
-         "readonly": true
+         "name": "Readings",
+         "type": "group",
+         "children": [
+            {
+               "name": "Temperature",
+               "type": "float",
+               "format": "{value:.4f} °C",
+               "readonly": true
+            },
+            {
+               "name": "Current through TEC",
+               "type": "float",
+               "suffix": "mA",
+               "decimals": 6,
+               "readonly": true
+            }
+         ]
       },
       {
          "name": "Output Config",
@@ -181,9 +187,15 @@
                   "field": "b"
                },
                "lock": false
-            },
+            }
+         ]
+      },
+      {
+         "name": "Postfilter Config",
+         "type": "group",
+         "children": [
             {
-               "name": "Postfilter Rate",
+               "name": "Rate",
                "type": "list",
                "value": 16.67,
                "thermostat:set_param": {