httpd/webdav: add a list of hosts allowed to send proxy headers

X-Forwarded-For, X-Real-IP and X-Forwarded-Proto headers will be ignored
for hosts not included in this list.

This is a backward incompatible change, before the proxy headers were
always used

templates/webadmin/base.html

@@ -209,6 +209,7 @@
         <i class="fas fa-angle-up"></i>
     </a>
 
+    {{if .LoggedAdmin.Username}}
     <!-- Logout Modal-->
     <div class="modal fade" id="logoutModal" tabindex="-1" role="dialog" aria-labelledby="modalLabel"
         aria-hidden="true">
@@ -228,6 +229,7 @@
             </div>
         </div>
     </div>
+    {{end}}
 
     {{block "dialog" .}}{{end}}