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

tests/Admin_Pages/Dashboard_Admin_Page_Test.php

@@ -36,7 +36,6 @@ class Dashboard_Admin_Page_Test extends WP_UnitTestCase {
 
 		// Verify localized script data is correct
 		$localized_vars = wp_scripts()->get_data('wu-dashboard-stats', 'data');
-		echo($localized_vars);
 		$this->assertStringContainsString('"month_list":["Jan ', $localized_vars);
 		$this->assertStringContainsString('"today":"', $localized_vars); // Check that today is included
 		$this->assertStringContainsString('"new_mrr":"New MRR"', $localized_vars);