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

sunrise.php

@@ -66,6 +66,8 @@ foreach ([$wu_sunrise, $wu_mu_sunrise] as $wu_sunrise_file) {
 	}
 }
 unset($wu_sunrise_file);
+unset($wu_mu_sunrise);
+unset($wu_sunrise);
 /**
  * Include Mercator.
  *
@@ -81,6 +83,7 @@ $wu_mercator = defined('WP_PLUGIN_DIR')
 if (file_exists($wu_mercator)) {
 	require $wu_mercator;
 }
+unset($wu_mercator);
 
 /**
  * Adds a warning when WP Multisite WaaS is not present but the sunrise file is.