Prep Plugin for release on WordPress.org (#23)

* Update translation text domain
* Escape everything that should be escaped.
* Add nonce checks where needed.
* Sanitize all inputs.
* Apply Code style changes across the codebase.
* Correct many deprecation notices.
* Optimize load order of many filters.
* Add Proper Build script
* Use emojii flags
* Fix i18n deprecation  notice for translating too early
* Put all scripts in footer and load async

inc/development/class-toolkit.php

@@ -125,7 +125,7 @@ class Toolkit {
 
 		$args = $manager->get_arguments_schema('update' === $context);
 
-		file_put_contents(wu_path("/mpb/data/endpoint/.endpoint-$class_name-$context"), json_encode($args)); // phpcs:ignore
+		file_put_contents(wu_path("/mpb/data/endpoint/.endpoint-$class_name-$context"), wp_json_encode($args)); // phpcs:ignore
 	}
 
 	/**