Add copyright headers and contributors list

Add proper copyright notices to all source files with accurate date
ranges per contributor based on git history. Add contributors to
composer.json authors and README.

ident_switch.php

@@ -1,12 +1,17 @@
 <?php
 /**
- * Identities IMAP
+ * ident_switch - Roundcube plugin for fast switching between accounts.
  *
- * This plugin allows fast switching between accounts.
+ * Copyright (C) 2016-2022 Boris Gulay
+ * Copyright (C) 2019      Christian Landvogt
+ * Copyright (C) 2021      Gergely Papp
+ * Copyright (C) 2022      Mickael
+ * Copyright (C) 2026      Gecka
  *
- * @version 4.4.2
- * @author Boris Gulay
- * @url 
+ * Original code licensed under GPL-3.0+.
+ * New contributions licensed under AGPL-3.0+.
+ *
+ * @url https://github.com/Gecka-apps/ident_switch
  */
 class ident_switch extends rcube_plugin
 {