Real-time communication with frontend

- Frontend shows heatmap of most visit places
- Maximum accuracy can now be set
- Fix bug where battery chart filtered values wrongly

backend/models/beat/beat.schema.ts

@@ -10,7 +10,8 @@ const schemaBeat = new Schema({
     createdAt: { type: SchemaTypes.Date, required: false }
 }, {
     timestamps: {
-        createdAt: true
+        createdAt: true,
+        updatedAt: false
     },
     versionKey: false
 });