Refactor user session handling and permissions management

- Updated session variables to use 'authorization' array instead of 'username' for user identification across multiple files.
- Introduced a new function `getUserPermissions` to consolidate user permissions retrieval based on assigned roles.
- Modified API calls to use the new authorization structure and updated endpoints to v2.
- Enhanced language support by adding 'PL' to the list of supported languages.
- Cleaned up redundant code and improved session management during user login and registration processes.
- Added a new API endpoint for fetching user permissions based on user ID.

factuur.php

@@ -1,7 +1,7 @@
 <?php
 defined(page_security_key) or exit;
 
-if (debug && debug_id == $_SESSION['id']) {
+if (debug && debug_id == $_SESSION['authorization']['id']) {
     ini_set('display_errors', '1');
     ini_set('display_startup_errors', '1');
     error_reporting(E_ALL);
@@ -11,7 +11,7 @@ include_once './assets/functions.php';
 include_once './settings/settings_redirector.php';
 
 // Check if allowed
-if (isAllowed('order', $_SESSION['profile'], $_SESSION['permission'], 'R') === 0) {
+if (isAllowed('order', $_SESSION['authorization']['profile'], $_SESSION['authorization']['permission'], 'R') === 0) {
     header('location: index.php');
     exit;
 }