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/dashboard-statistics/widget-mrr-growth.php

@@ -11,7 +11,7 @@
 
 	<span class="wu-blinking-animation">
 
-		<?php _e('Loading...', 'wp-ultimo'); ?>
+		<?php esc_html_e('Loading...', 'wp-multisite-waas'); ?>
 
 	</span>