/custom_action
list only custom skins

Sourcecode in SkinMgr/actions.js:
1:   function custom_action() {
2:      res.data.title = getMessage("SkinMgr.listCustomTitle", {layoutTitle: this._parent.title});
3:      res.data.list = this.renderList(this.getCustomSkins(), req.action);
4:      res.data.body = this.renderSkinAsString("main");
5:      res.handlers.context.renderSkin("page");
6:      return;
7:   }