Security fix: unauthorized access (#10091)

* Security fix: unauthorized access
Affects nginx users:
Moved php files outside of public html directory (Apache was protected by .htaccess)

Affects all users:
Some files did not check for authentication and could disclose some info.
Better checks before including files from user input

* git mv html/includes/ includes/html
git mv html/pages/ includes/html/

includes/html/pages/plugin.inc.php

@@ -0,0 +1,23 @@
+<?php
+
+use LibreNMS\Config;
+
+$link_array = array('page' => 'plugin');
+
+$pagetitle[] = 'Plugin';
+
+if ($vars['view'] == 'admin') {
+    include_once Config::get('install_dir') . '/includes/html/pages/plugin/admin.inc.php';
+} else {
+    $plugin = dbFetchRow("SELECT `plugin_name` FROM `plugins` WHERE `plugin_name` = ? AND `plugin_active`='1'", [$vars['p']]);
+    if (!empty($plugin)) {
+        $plugin_path = Config::get('plugin_dir').'/'.$plugin['plugin_name'].'/'.$plugin['plugin_name'].'.inc.php';
+        if (is_file($plugin_path)) {
+            chdir(Config::get('install_dir') . '/html');
+            include $plugin_path;
+            chdir(Config::get('install_dir'));
+            return;
+        }
+    }
+    print_error('This plugin is either disabled or not available.');
+}