Layout: Masonry/Packed Layout

### Description

We should, as a minimum, offer the "Packed" layout as per Dashboard 1.0. On the surface, it looks like a simple CSS Flex layout, but will fill space vertically too, whereas Flex will only move content to a new row, where a given row's height is defined by the tallest element in that row.

### Have you provided an initial effort estimate for this issue?

I have provided an initial effort estimate