tweak code formatting rules

* output as "json-stringify" (which is most similar to most files currently in the repository)
* add .editorconfig
* drop (now) superfluous pretter settings
* add npm commands to check code style

package.json

@@ -11,12 +11,15 @@
   "license": "ISC",
   "main": "build.js",
   "scripts": {
+    "lint": "prettier --check data",
+    "lint:fix": "prettier --write data",
     "build": "node scripts/build.js",
     "dist": "node scripts/dist.js",
     "test": "node scripts/test.js",
     "translations": "node scripts/translations.js"
   },
   "devDependencies": {
-    "@ideditor/schema-builder": "~4.0.5"
+    "@ideditor/schema-builder": "~4.0.5",
+    "prettier": "~2.5.1"
   }
 }