login, signup: redirect to dashboard if logged in

Fixes https://gitlab.com/commento/commento-ce/issues/60

frontend/js/auth-common.js

@@ -1,5 +1,14 @@
 (function (global, document) {
 
+  // Redirect the user to the dashboard if there's a cookie. If the cookie is
+  // invalid, they would be redirected back to the login page *after* the
+  // cookie is deleted.
+  global.loggedInRedirect = function() {
+    if (global.cookieGet("commentoOwnerToken") !== undefined)
+      document.location = "/dashboard";
+  }
+
+
   // Prefills the email field from the URL parameter.
   global.prefillEmail = function() {
     if (paramGet("email") != undefined) {

frontend/login.html

@@ -16,6 +16,7 @@
 
   <script>
   window.onload = function() {
+    window.loggedInRedirect();
     window.prefillEmail();
     window.displayMessages();
   };

frontend/signup.html

@@ -16,6 +16,7 @@
 
   <script>
   window.onload = function() {
+    window.loggedInRedirect();
     window.prefillEmail();
   };
   </script>