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.

report_contracts_billing.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);  
@@ -18,7 +18,7 @@ $prev_page = ($_SESSION['origin'] == 'equipments') ? $_SESSION['prev_origin_equi
 $back_btn_orgin =  ($prev_page != '')? '<a href="'.$prev_page.'" class="btn alt mar-right-2">←</a>':'';
 
 //Check if allowed
-if (isAllowed($page,$_SESSION['profile'],$_SESSION['permission'],'R') === 0){
+if (isAllowed($page,$_SESSION['authorization']['profile'],$_SESSION['authorization']['permission'],'R') === 0){
     header('location: index.php');
     exit;
 }