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/class-ajax.php

@@ -100,7 +100,7 @@ class Ajax {
 		}
 
 		$args = wp_parse_args(
-			$_REQUEST,
+			$_REQUEST, // phpcs:ignore WordPress.Security.NonceVerification.Recommended
 			[
 				'model'   => 'membership',
 				'query'   => [],