Feature request: gallery page generator

## Check List

Please check followings before submitting a new feature request.

- [x] I have already read [Docs page](https://hexo.io/docs/)
- [x] I have already searched existing issues

## Feature Request

Is it possible to have a `hexo-generator-gallery` plugin that create a gallery page which index all the photos used in the published articles, namely, an archive page for photos used in all posts, similar to what `hexo-generator-archive` did for the posts or what`hexo-generator-tag` did for tags.
And it would be better to have a timeline that sort the photos with the published time of the post in which these photos appeared.