FEATURE: Allow admins to lock users from TL3 promotion/demotion

Also, update the display logic for the leader promotion screen to
account for the demotion grace period.

app/assets/javascripts/admin/models/admin_user.js

@@ -164,6 +164,24 @@ Discourse.AdminUser = Discourse.User.extend({
     this.set('trustLevel.id', this.get('originalTrustLevel'));
   },
 
+  lockTrustLevel: function(locked) {
+    Discourse.ajax("/admin/users/" + this.id + "/trust_level_lock", {
+      type: 'PUT',
+      data: { locked: !!locked }
+    }).then(function() {
+      // succeeded
+      window.location.reload();
+    }, function(e) {
+      // failure
+      var error;
+      if (e.responseJSON && e.responseJSON.errors) {
+        error = e.responseJSON.errors[0];
+      }
+      error = error || I18n.t('admin.user.trust_level_change_failed', { error: "http: " + e.status + " - " + e.body });
+      bootbox.alert(error);
+    });
+  },
+
   isSuspended: Em.computed.equal('suspended', true),
   canSuspend: Em.computed.not('staff'),