relax access to admin action

Since we want to check the access to the Admin plugins on an individual
basis, we need to grant access to all logged in users at first. This
means a user could access the admin page, but would not see any plugins
available.

inc/Action/Admin.php

@@ -15,22 +15,11 @@ class Admin extends AbstractUserAction {
 
     /** @inheritdoc */
     public function minimumPermission() {
-        global $INFO;
-
-        if($INFO['ismanager']) {
-            return AUTH_READ; // let in check later
-        } else {
-            return AUTH_ADMIN;
-        }
+        return AUTH_READ; // let in check later
     }
 
     public function checkPreconditions() {
         parent::checkPreconditions();
-
-        global $INFO;
-        if(!$INFO['ismanager']) {
-            throw new ActionException('denied');
-        }
     }
 
     public function preProcess() {