Masonry-style catalog with CSS3

[DangerOnTheRanger]

While currently only implemented in Firefox, if CSS3's grid-template-rows: masonry gains widespread adoption, then the old masonry-style catalog that Maniwani had (still shown in the README...) can be fully brought back for clients with and without JS-enabled, also removing the need to have a fallback no-JS catalog implementation. I'm making this issue as a way to track that possibility.