Updated package.json & added various config files.

.eslintrc.js

@@ -0,0 +1,25 @@
+/* eslint-env node */
+
+'use strict';
+
+module.exports = {
+	extends: 'ckeditor5',
+	root: true,
+	rules: {
+		// This rule disallows importing core DLL packages directly. Imports should be done using the `ckeditor5` package.
+		// Also, importing non-DLL packages is not allowed. If the package requires other features to work, they should be
+		// specified as soft-requirements.
+		// Read more: https://ckeditor.com/docs/ckeditor5/latest/builds/guides/migration/migration-to-26.html#soft-requirements.
+		'ckeditor5-rules/ckeditor-imports': 'error'
+	},
+	overrides: [
+		{
+			files: [ 'tests/**/*.js', 'sample/**/*.js' ],
+			rules: {
+				// To write complex tests, you may need to import files that are not exported in DLL files by default.
+				// Hence, imports CKEditor 5 packages in test files are not checked.
+				'ckeditor5-rules/ckeditor-imports': 'off'
+			}
+		}
+	]
+};