refactor: sensor configuration fields

Automatically round decimal values for sensor.x and .y to an integer.
Make fields optional which are not used in every sensor.

doc/sensor_mode2_fan.md

@@ -31,7 +31,6 @@ Example `panel.json` with a single "fan" indicator sensor and the following (par
       "id": "29d9ef2d-30b4-459d-b2b0-43cb6d4d6b41",
       "itemName": "CPU usage",
       "mode": 2,
-      "type": 1,
       "direction": 1,
       "label": "cpu_percent",
       "value": "47.7",
@@ -39,10 +38,6 @@ Example `panel.json` with a single "fan" indicator sensor and the following (par
       "y": 184,
       "width": 237,
       "height": 237,
-      "fontColor": "#ffffff",
-      "fontSize": 14,
-      "fontFamily": "default_font",
-      "textAlign": "left",
       "minAngle": -160,
       "maxAngle": 30,
       "minValue": 0,