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/functions/compatiblity.php

@@ -0,0 +1,35 @@
+<?php
+/**
+ * Backport of WordPress 6.7.0 current_user_can_for_site() function.
+ *
+ * @package WP_Ultimo
+ */
+
+if ( ! function_exists('current_user_can_for_site')) {
+
+	/**
+	 * Returns whether the current user has the specified capability for a given site.
+	 *
+	 * This function also accepts an ID of an object to check against if the capability is a meta capability. Meta
+	 * capabilities such as `edit_post` and `edit_user` are capabilities used by the `map_meta_cap()` function to
+	 * map to primitive capabilities that a user or role has, such as `edit_posts` and `edit_others_posts`.
+	 *
+	 * This function replaces the current_user_can_for_blog() function.
+	 *
+	 * Example usage:
+	 *
+	 *     current_user_can_for_site( $site_id, 'edit_posts' );
+	 *     current_user_can_for_site( $site_id, 'edit_post', $post->ID );
+	 *     current_user_can_for_site( $site_id, 'edit_post_meta', $post->ID, $meta_key );
+	 *
+	 * @since 6.7.0
+	 *
+	 * @param int    $site_id    Site ID.
+	 * @param string $capability Capability name.
+	 * @param mixed  ...$args    Optional further parameters, typically starting with an object ID.
+	 * @return bool Whether the user has the given capability.
+	 */
+	function current_user_can_for_site($site_id, $capability, ...$args) { // phpcs:ignore WordPress.NamingConventions.PrefixAllGlobals.NonPrefixedFunctionFound
+		return current_user_can_for_blog($site_id, $capability, ...$args);
+	}
+}