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/helpers/validation-rules/class-products.php

@@ -55,7 +55,7 @@ class Products extends Rule {
 			return true;
 		}
 
-		$this->message = __('A plan is required.', 'wp-ultimo');
+		$this->message = __('A plan is required.', 'wp-multisite-waas');
 
 		return false;
 	}