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

views/base/wizard/submit-box.php

@@ -9,13 +9,13 @@
 <div class="wu-flex wu-justify-between wu-bg-gray-100 wu--m-in wu-mt-4 wu-p-4 wu-overflow-hidden wu-border-t wu-border-solid wu-border-l-0 wu-border-r-0 wu-border-b-0 wu-border-gray-300">
 
 	<a href="<?php echo esc_url($page->get_prev_section_link()); ?>" class="wu-self-center button button-large wu-float-left">
-	<?php _e('&larr; Go Back', 'wp-ultimo'); ?>
+	<?php esc_html_e('← Go Back', 'wp-multisite-waas'); ?>
 	</a>
 
 	<span class="wu-self-center wu-content-center wu-flex">
 
 	<button name="submit" value="1" class="button button-primary button-large">
-		<?php _e('Continue', 'wp-ultimo'); ?>
+		<?php esc_html_e('Continue', 'wp-multisite-waas'); ?>
 	</button>
 
 	</span>