Make the Administration menu item be show/hide-driven.

Always render the Administration menu item from the back end, but
make it be hidden by default until the page is loaded.  Then, the
client can un-hide it as needed.

(imported from commit 66e607eec430d7179b4d5ac3f5416f5be8ac26c9)

static/js/admin.js

@@ -2,6 +2,15 @@ var admin = (function () {
 
 var exports = {};
 
+exports.show_or_hide_menu_item = function () {
+    var item = $('.admin-menu-item').expectOne();
+    if (page_params.is_admin) {
+        item.show();
+    } else {
+        item.hide();
+    }
+};
+
 function failed_listing_users(xhr, error) {
     util.destroy_loading_indicator($('#subs_page_loading_indicator'));
     ui.report_error("Error listing users or bots", xhr, $("#administration-status"));

static/js/ui.js

@@ -966,6 +966,8 @@ $(function () {
         $('#old_password, #new_password, #confirm_password').val('');
     }
 
+    admin.show_or_hide_menu_item();
+
     $('#gear-menu a[data-toggle="tab"]').on('show', function (e) {
         // Save the position of our old tab away, before we switch
         var old_tab = $(e.relatedTarget).attr('href');

static/styles/zulip.css

@@ -3699,6 +3699,10 @@ div.edit_bot {
     text-decoration: line-through;
 }
 
+.admin-menu-item {
+    display: none;
+}
+
 .administration {
     margin-top: 55px;
     padding-left: 15px;

templates/zerver/navbar.html

@@ -82,13 +82,11 @@
                     </a>
                   </li>
                   <li class="divider"></li>
-                  {% if is_admin %}
-                  <li title="Administration">
+                  <li title="Administration" class="admin-menu-item">
                     <a href="#administration" role="button" data-toggle="tab">
                       <i class="icon-vector-bolt"></i> Administration
                     </a>
                   </li>
-                  {% endif %}
                   {% if show_invites %}
                   <li title="Invite coworkers to Zulip">
                     <a href="#invite-user" role="button" data-toggle="modal">