Add administrative panel to allow for user deactivations etc.

We now show a list of users and allow you to deactivate a user using the
same process as `python manage.py deactivate_user`.

We add a new menu item accessible from the gear icon which will eventually
have much more than just this, but we have a good start here.

Here we also add a property to UserProfile which determines whether you're
eligible to access the administration panel, and then have code which shows
the menu option if so.

This introduces a new JS file, admin.js.

(imported from commit 52296fdedb46b4f32d541df43022ffccfb277297)

static/js/ui.js

@@ -858,6 +858,9 @@ $(function () {
     // Whenever the streams page comes up (from anywhere), populate it.
     subs_link.on('shown', subs.setup_page);
 
+    var admin_link = $('#gear-menu a[href="#administration"]');
+    admin_link.on('shown', admin.setup_page);
+
     $('#pw_change_link').on('click', function (e) {
         e.preventDefault();
         $('#pw_change_link').hide();