collections browser , enhance with thumbnails

in the 'public collections' screen, it would be nice to show a few images from the collection, to give more of an idea whats in there, and perhaps some of the existing labels used in it
(perhaps show the most common labels, and the most-labelled images)

从公开集合屏幕开始，跟踪集合图像和标签当前的加载与渲染方式。定义一小组具有代表性的缩略图和常用标签，然后确认该屏幕能为访客提供每个集合的有用预览。

由索引模型根据 Issue 内容生成。