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/hashchange.js

@@ -130,6 +130,9 @@ function do_hashchange() {
         case "#subscriptions":
             ui.change_tab_to("#subscriptions");
             break;
+        case "#administration":
+            ui.change_tab_to("#administration");
+            break;
         case "#settings":
             ui.change_tab_to("#settings");
             break;