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)

zerver/views.py

@@ -659,7 +659,8 @@ def home(request):
                                'nofontface': is_buggy_ua(request.META["HTTP_USER_AGENT"]),
                                'show_debug':
                                    settings.DEBUG and ('show_debug' in request.GET),
-                               'show_invites': show_invites
+                               'show_invites': show_invites,
+                               'show_admin': user_profile.show_admin,
                                },
                               context_instance=RequestContext(request))