Fix Firefox silently deleted tunnels

Debugging notes:

* The act of refreshing a page can delete tunnels created by other UI
  sessions, I think because it has local CSS checkbox state.
  * Happens on firefox desktop and mobile. Here's how to reproduce:
    1. Load the UI in Chrome and FF.
    2. Delete the last tunnel from FF.
    3. Add it back in Chrome.
    4. Refresh FF. The tunnel will be silently deleted.
  * I'm pretty sure this is bugged behavior in FF, because the checkboxes have
    completely unique ids, but it's treating them like the same checkbox.
  * Setting autocomplete='off' on the input elements seems to fix the problem.
    Not sure if it will work correctly in all browsers.

todo.md

@@ -14,5 +14,3 @@
   is wrong when domain stuff breaks.
 * Responses to unauthorized requests are leaking information about the current
   tunnels through the genereated CSS.
-* The act of refreshing a page can delete tunnels created by other UI
-  sessions, I think because it has local CSS checkbox state.

webui/index.tmpl

@@ -21,7 +21,7 @@
         <div class='content'>
           <div class='list'>
             {{range $domain, $tunnel:= .Tunnels}}
-            <input type='checkbox' class='toggle' id='toggle-tunnel-hide-deleted-{{$tunnel.CssId}}'>
+            <input autocomplete='off' type='checkbox' class='toggle' id='toggle-tunnel-hide-deleted-{{$tunnel.CssId}}'>
             <div class='list-item'>
               <div>
                 <a href="https://{{$domain}}">{{$domain}}</a>:{{$tunnel.TunnelPort}} -> {{$tunnel.ClientName}}:{{$tunnel.ClientPort}}
@@ -32,7 +32,7 @@
               </label>
             </div>
 
-            <input type='checkbox' id='toggle-tunnel-delete-dialog-{{$tunnel.CssId}}'>
+            <input autocomplete='off' type='checkbox' id='toggle-tunnel-delete-dialog-{{$tunnel.CssId}}'>
             <div class='confirm-dialog'>
               <label for='toggle-tunnel-delete-dialog-{{$tunnel.CssId}}' class='confirm-dialog__overlay'></label>