Monitor Page Preheat values

Change the default preheat values to the Initial Layer values.

resources/qml/PrintMonitor.qml

@@ -129,7 +129,7 @@ ScrollView
         {
             id: bedTemperature
             containerStack: Cura.MachineManager.activeMachine
-            key: "material_bed_temperature"
+            key: "material_bed_temperature_layer_0"
             watchedProperties: ["value", "minimum_value", "maximum_value", "resolve"]
             storeIndex: 0
         }

resources/qml/PrinterOutput/ExtruderBox.qml

@@ -22,7 +22,7 @@ Item
     {
         id: extruderTemperature
         containerStackId: Cura.ExtruderManager.extruderIds[position]
-        key: "material_print_temperature"
+        key: "material_print_temperature_layer_0"
         watchedProperties: ["value", "minimum_value", "maximum_value", "resolve"]
         storeIndex: 0
     }