Add Global Readonly (#158)

Added a global readonly variable that will force readonly mode both when
not using the auth system and for all users if the auth system is being
used.

Co-authored-by: Prasath Mani <prasathmani@users.noreply.github.com>

tinyfilemanager.php

@@ -36,6 +36,13 @@ $readonly_users = array(
     'user'
 );
 
+// Global readonly, including when auth is not being used
+$global_readonly = false;
+
+// user specific directories
+// array('Username' => 'Directory path', 'Username2' => 'Directory path', ...)
+$directories_users = array();
+
 // Enable highlight.js (https://highlightjs.org/) on view's page
 $use_highlightjs = true;