re-authenticate api when user data changes (closes #137)

this re-authenticates a bit more often than necessary, but I think it's fine for now

src/c3nav/site/static/site/js/c3nav.js

@@ -1736,6 +1736,7 @@ c3nav = {
         window.location.reload();
     },
     _set_user_data: function (data) {
+        c3nav_api.authenticate();
         c3nav.user_data = data;
         var $user = $('header #user');
         $user.find('span').text(data.title);

src/c3nav/static/c3nav/js/api.js

@@ -5,7 +5,11 @@
 
         constructor(base ) {
             this.base = base;
-            this.auth_promise = fetch(this.base+'auth/session/', {
+            this.auth_promise = this.authenticate();
+        }
+
+        authenticate() {
+            return fetch(this.base+'auth/session/', {
                 credentials: 'include',
                 method: 'GET',
             })