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_mode4_pointer.md

@@ -31,7 +31,6 @@ Example `panel.json` with a single "pointer" indicator sensor and the following
       "id": "a9d4acac-2af9-4fe0-9f69-86cd09f25696",
       "itemName": "CPU dial",
       "mode": 4,
-      "type": 1,
       "direction": 1,
       "label": "cpu_percent",
       "value": "47.7",
@@ -39,11 +38,6 @@ Example `panel.json` with a single "pointer" indicator sensor and the following
       "y": 208,
       "width": 302,
       "height": 302,
-      "fontColor": "#ffffff",
-      "fontSize": 14,
-      "fontFamily": "",
-      "fontWeight": "normal",
-      "textAlign": "left",
       "minAngle": -110,
       "maxAngle": 110,
       "minValue": 0,