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/models/interface-limitable.php

@@ -0,0 +1,99 @@
+<?php
+/**
+ * Limitable interface.
+ *
+ * @package WP_Ultimo
+ * @subpackage Models
+ */
+
+namespace WP_Ultimo\Models;
+
+interface Limitable {
+	/**
+	 * List of limitations that need to be merged.
+	 *
+	 * Every model that is limitable (imports this trait)
+	 * needs to declare explicitly the limitations that need to be
+	 * merged. This allows us to chain the merges, and gives us
+	 * a final list of limitations at the end of the process.
+	 *
+	 * @since 2.0.0
+	 * @return array
+	 */
+	public function limitations_to_merge();
+
+	/**
+	 * Returns the limitations of this particular blog.
+	 *
+	 * @since 2.0.0
+	 *
+	 * @param bool $waterfall If we should construct the limitations object recursively.
+	 * @param bool $skip_self If we should skip the current limitations.
+	 * @return \WP_Ultimo\Objects\Limitations
+	 */
+	public function get_limitations($waterfall = true, $skip_self = false);
+
+
+	/**
+	 * Checks if this site has limitations or not.
+	 *
+	 * @since 2.0.0
+	 * @return boolean
+	 */
+	public function has_limitations();
+
+	/**
+	 * Checks if a particular module is being limited.
+	 *
+	 * @since 2.0.0
+	 *
+	 * @param string $module Module to check.
+	 * @return boolean
+	 */
+	public function has_module_limitation($module);
+
+	/**
+	 * Returns all user role quotas.
+	 *
+	 * @since 2.0.0
+	 * @return array
+	 */
+	public function get_user_role_quotas();
+
+	/**
+	 * Proxy method to retrieve the allowed user roles.
+	 *
+	 * @since 2.0.0
+	 * @return array
+	 */
+	public function get_allowed_user_roles();
+
+	/**
+	 * Schedules plugins to be activated or deactivated based on the current limitations;
+	 *
+	 * @since 2.0.5
+	 * @return void
+	 */
+	public function sync_plugins(): void;
+
+	/**
+	 * Makes sure we save limitations when we are supposed to.
+	 *
+	 * This is called on the handle_save method of the inc/admin-pages/class-edit-admin-page.php
+	 * for all models that have the trait Limitable.
+	 *
+	 * @see inc/admin-pages/class-edit-admin-page.php
+	 *
+	 * @since 2.0.0
+	 * @return void
+	 */
+	public function handle_limitations(): void;
+
+	/**
+	 * Returns the list of product slugs associated with this model.
+	 *
+	 * @since 2.0.0
+	 * @return array
+	 */
+	public function get_applicable_product_slugs();
+}